Copying Data Using References To The Data

ABSTRACT

Copying data using references to the data, including: receiving a request to write the source data to a target volume, wherein the request to write the source data indicates the reference information; obtaining a metadata representation of the source data using the reference information; an copying, using the reference information, the metadata representation of the source data to the target volume.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application for patent entitled to a filing dateand claiming the benefit of earlier-filed U.S. Patent Application No.17/471,607, filed Sep. 10, 2021, which is a continuation of U.S. PatentNo. 11,126,381, issued Sep. 21, 2021, which is a continuation of U.S.Patent No. 10,459,664, issued Oct. 29, 2019, which claims priority fromU.S. Provisional Patent Application Serial No. 62/483,897, filed Apr.10, 2017, each of which is hereby incorporated by reference in theirentirety.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A illustrates a first example system for data storage.

FIG. 1B illustrates a second example system for data storage.

FIG. 1C illustrates a third example system for data storage.

FIG. 1D illustrates a fourth example system for data storage.

FIG. 2A is a perspective view of a storage cluster with multiple storagenodes and internal storage coupled to each storage node to providenetwork attached storage.

FIG. 2B is a block diagram showing an interconnect switch couplingmultiple storage nodes in accordance with some embodiments.

FIG. 2C is a multiple level block diagram, showing contents of a storagenode and contents of one of the non-volatile solid state storage units.

FIG. 2D shows a storage server environment, which uses embodiments ofthe storage nodes and storage units of some previous figures inaccordance with some embodiments.

FIG. 2E is a blade hardware block diagram, showing a control plane,compute and storage planes, and authorities interacting with underlyingphysical resources.

FIG. 2F depicts elasticity software layers in blades of a storagecluster.

FIG. 2G depicts authorities and storage resources in blades of a storagecluster.

FIG. 3A sets forth a diagram of a storage system that is coupled fordata communications with a cloud services provider.

FIG. 3B sets forth a diagram of a storage system.

FIG. 3C sets forth a diagram of metadata representations within astorage system.

FIG. 4 sets forth a flow chart illustrating an example method for avirtualized copy-by-reference according to some embodiments of thepresent disclosure.

FIG. 5 sets forth a flow chart illustrating an example method for avirtualized copy-by-reference according to some embodiments of thepresent disclosure.

FIG. 6 sets forth a flow chart illustrating an example method for avirtualized copy-by-reference according to some embodiments of thepresent disclosure.

FIG. 7 sets forth a flow chart illustrating an example method for avirtualized copy-by-reference according to some embodiments of thepresent disclosure.

FIG. 8 sets forth a flow chart illustrating an example method for avirtualized copy-by-reference according to some embodiments of thepresent disclosure.

DESCRIPTION OF EMBODIMENTS

Example methods, apparatus, and products for virtualizedcopy-by-reference in accordance with embodiments of the presentdisclosure are described with reference to the accompanying drawings,beginning with FIG. 1A. FIG. 1A illustrates an example system for datastorage, in accordance with some implementations. System 100 (alsoreferred to as “storage system” herein) includes numerous elements forpurposes of illustration rather than limitation. It may be noted thatsystem 100 may include the same, more, or fewer elements configured inthe same or different manner in other implementations.

System 100 includes a number of computing devices 164A-B. Computingdevices (also referred to as “client devices” herein) may be embodied,for example, a server in a data center, a workstation, a personalcomputer, a notebook, or the like. Computing devices 164A-B may becoupled for data communications to one or more storage arrays 102A-Bthrough a storage area network (‘SAN’) 158 or a local area network(‘LAN’) 160.

The SAN 158 may be implemented with a variety of data communicationsfabrics, devices, and protocols. For example, the fabrics for SAN 158may include Fibre Channel, Ethernet, Infiniband, Serial Attached SmallComputer System Interface (′SAS′), or the like. Data communicationsprotocols for use with SAN 158 may include Advanced TechnologyAttachment (‘ATA’), Fibre Channel Protocol, Small Computer SystemInterface (‘SCSI’), Internet Small Computer System Interface (‘iSCSI’),HyperSCSI, Non-Volatile Memory Express (‘NVMe’) over Fabrics, or thelike. It may be noted that SAN 158 is provided for illustration, ratherthan limitation. Other data communication couplings may be implementedbetween computing devices 164A-B and storage arrays 102A-B.

The LAN 160 may also be implemented with a variety of fabrics, devices,and protocols. For example, the fabrics for LAN 160 may include Ethernet(802.3), wireless (802.11), or the like. Data communication protocolsfor use in LAN 160 may include Transmission Control Protocol (‘TCP’),User Datagram Protocol (‘UDP’), Internet Protocol (‘IP’), HyperTextTransfer Protocol (‘HTTP’), Wireless Access Protocol (‘WAP’), HandheldDevice Transport Protocol (′HDTP′), Session Initiation Protocol (′SIP′),Real Time Protocol (‘RTP’), or the like.

Storage arrays 102A-B may provide persistent data storage for thecomputing devices 164A-B. Storage array 102A may be contained in achassis (not shown), and storage array 102B may be contained in anotherchassis (not shown), in implementations. Storage array 102A and 102B mayinclude one or more storage array controllers 110 (also referred to as“controller” herein). A storage array controller 110 may be embodied asa module of automated computing machinery comprising computer hardware,computer software, or a combination of computer hardware and software.In some implementations, the storage array controllers 110 may beconfigured to carry out various storage tasks. Storage tasks may includewriting data received from the computing devices 164A-B to storage array102A-B, erasing data from storage array 102A-B, retrieving data fromstorage array 102A-B and providing data to computing devices 164A-B,monitoring and reporting of disk utilization and performance, performingredundancy operations, such as Redundant Array of Independent Drives(‘RAID’) or RAID-like data redundancy operations, compressing data,encrypting data, and so forth.

Storage array controller 110 may be implemented in a variety of ways,including as a Field Programmable Gate Array (‘FPGA’), a ProgrammableLogic Chip (‘PLC’), an Application Specific Integrated Circuit (‘ASIC’),System-on-Chip (‘SOC’), or any computing device that includes discretecomponents such as a processing device, central processing unit,computer memory, or various adapters. Storage array controller 110 mayinclude, for example, a data communications adapter configured tosupport communications via the SAN 158 or LAN 160. In someimplementations, storage array controller 110 may be independentlycoupled to the LAN 160. In implementations, storage array controller 110may include an I/O controller or the like that couples the storage arraycontroller 110 for data communications, through a midplane (not shown),to a persistent storage resource 170A-B (also referred to as a “storageresource” herein). The persistent storage resource 170A-B main includeany number of storage drives 171A-F (also referred to as “storagedevices” herein) and any number of non-volatile Random Access Memory(‘NVRAM’) devices (not shown).

In some implementations, the NVRAM devices of a persistent storageresource 170A-B may be configured to receive, from the storage arraycontroller 110, data to be stored in the storage drives 171A-F. In someexamples, the data may originate from computing devices 164A-B. In someexamples, writing data to the NVRAM device may be carried out morequickly than directly writing data to the storage drive 171A-F. Inimplementations, the storage array controller 110 may be configured toutilize the NVRAM devices as a quickly accessible buffer for datadestined to be written to the storage drives 171A-F. Latency for writerequests using NVRAM devices as a buffer may be improved relative to asystem in which a storage array controller 110 writes data directly tothe storage drives 171A-F. In some implementations, the NVRAM devicesmay be implemented with computer memory in the form of high bandwidth,low latency RAM. The NVRAM device is referred to as “non-volatile”because the NVRAM device may receive or include a unique power sourcethat maintains the state of the RAM after main power loss to the NVRAMdevice. Such a power source may be a battery, one or more capacitors, orthe like. In response to a power loss, the NVRAM device may beconfigured to write the contents of the RAM to a persistent storage,such as the storage drives 171A-F.

In implementations, storage drive 171A-F may refer to any deviceconfigured to record data persistently, where “persistently” or“persistent” refers to a device’s ability to maintain recorded dataafter loss of power. In some implementations, storage drive 171A-F maycorrespond to non-disk storage media. For example, the storage drive171A-F may be one or more solid-state drives (‘SSDs’), flash memorybased storage, any type of solid-state non-volatile memory, or any othertype of non-mechanical storage device. In other implementations, storagedrive 171A-F may include mechanical or spinning hard disk, such ashard-disk drives (‘HDD’).

In some implementations, the storage array controllers 110 may beconfigured for offloading device management responsibilities fromstorage drive 171A-F in storage array 102A-B. For example, storage arraycontrollers 110 may manage control information that may describe thestate of one or more memory blocks in the storage drives 171A-F. Thecontrol information may indicate, for example, that a particular memoryblock has failed and should no longer be written to, that a particularmemory block contains boot code for a storage array controller 110, thenumber of program-erase (‘P/E’) cycles that have been performed on aparticular memory block, the age of data stored in a particular memoryblock, the type of data that is stored in a particular memory block, andso forth. In some implementations, the control information may be storedwith an associated memory block as metadata. In other implementations,the control information for the storage drives 171A-F may be stored inone or more particular memory blocks of the storage drives 171A-F thatare selected by the storage array controller 110. The selected memoryblocks may be tagged with an identifier indicating that the selectedmemory block contains control information. The identifier may beutilized by the storage array controllers 110 in conjunction withstorage drives 171A-F to quickly identify the memory blocks that containcontrol information. For example, the storage controllers 110 may issuea command to locate memory blocks that contain control information. Itmay be noted that control information may be so large that parts of thecontrol information may be stored in multiple locations, that thecontrol information may be stored in multiple locations for purposes ofredundancy, for example, or that the control information may otherwisebe distributed across multiple memory blocks in the storage drive171A-F.

In implementations, storage array controllers 110 may offload devicemanagement responsibilities from storage drives 171A-F of storage array102A-B by retrieving, from the storage drives 171A-F, controlinformation describing the state of one or more memory blocks in thestorage drives 171A-F. Retrieving the control information from thestorage drives 171A-F may be carried out, for example, by the storagearray controller 110 querying the storage drives 171A-F for the locationof control information for a particular storage drive 171A-F. Thestorage drives 171A-F may be configured to execute instructions thatenable the storage drive 171A-F to identify the location of the controlinformation. The instructions may be executed by a controller (notshown) associated with or otherwise located on the storage drive 171A-Fand may cause the storage drive 171A-F to scan a portion of each memoryblock to identify the memory blocks that store control information forthe storage drives 171A-F. The storage drives 171A-F may respond bysending a response message to the storage array controller 110 thatincludes the location of control information for the storage drive171A-F. Responsive to receiving the response message, storage arraycontrollers 110 may issue a request to read data stored at the addressassociated with the location of control information for the storagedrives 171A-F.

In other implementations, the storage array controllers 110 may furtheroffload device management responsibilities from storage drives 171A-F byperforming, in response to receiving the control information, a storagedrive management operation. A storage drive management operation mayinclude, for example, an operation that is typically performed by thestorage drive 171A-F (e.g., the controller (not shown) associated with aparticular storage drive 171A-F). A storage drive management operationmay include, for example, ensuring that data is not written to failedmemory blocks within the storage drive 171A-F, ensuring that data iswritten to memory blocks within the storage drive 171A-F in such a waythat adequate wear leveling is achieved, and so forth.

In implementations, storage array 102A-B may implement two or morestorage array controllers 110. For example, storage array 102A mayinclude storage array controllers 110A and storage array controllers110B. At a given instance, a single storage array controller 110 (e.g.,storage array controller 110A) of a storage system 100 may be designatedwith primary status (also referred to as “primary controller” herein),and other storage array controllers 110 (e.g., storage array controller110A) may be designated with secondary status (also referred to as“secondary controller” herein). The primary controller may haveparticular rights, such as permission to alter data in persistentstorage resource 170A-B (e.g., writing data to persistent storageresource 170A-B). At least some of the rights of the primary controllermay supersede the rights of the secondary controller. For instance, thesecondary controller may not have permission to alter data in persistentstorage resource 170A-B when the primary controller has the right. Thestatus of storage array controllers 110 may change. For example, storagearray controller 110A may be designated with secondary status, andstorage array controller 110B may be designated with primary status.

In some implementations, a primary controller, such as storage arraycontroller 110A, may serve as the primary controller for one or morestorage arrays 102A-B, and a second controller, such as storage arraycontroller 110B, may serve as the secondary controller for the one ormore storage arrays 102A-B. For example, storage array controller 110Amay be the primary controller for storage array 102A and storage array102B, and storage array controller 110B may be the secondary controllerfor storage array 102A and 102B. In some implementations, storage arraycontrollers 110C and 110D (also referred to as “storage processingmodules”) may neither have primary or secondary status. Storage arraycontrollers 110C and 110D, implemented as storage processing modules,may act as a communication interface between the primary and secondarycontrollers (e.g., storage array controllers 110A and 110B,respectively) and storage array 102B. For example, storage arraycontroller 110A of storage array 102A may send a write request, via SAN158, to storage array 102B. The write request may be received by bothstorage array controllers 110C and 110D of storage array 102B. Storagearray controllers 110C and 110D facilitate the communication, e.g., sendthe write request to the appropriate storage drive 171A-F. It may benoted that in some implementations storage processing modules may beused to increase the number of storage drives controlled by the primaryand secondary controllers.

In implementations, storage array controllers 110 are communicativelycoupled, via a midplane (not shown), to one or more storage drives171A-F and to one or more NVRAM devices (not shown) that are included aspart of a storage array 102A-B. The storage array controllers 110 may becoupled to the midplane via one or more data communication links and themidplane may be coupled to the storage drives 171A-F and the NVRAMdevices via one or more data communications links. The datacommunications links described herein are collectively illustrated bydata communications links 108A-D and may include a Peripheral ComponentInterconnect Express (‘PCIe’) bus, for example.

FIG. 1B illustrates an example system for data storage, in accordancewith some implementations. Storage array controller 101 illustrated inFIG. 1B may be similar to the storage array controllers 110 describedwith respect to FIG. 1A. In one example, storage array controller 101may be similar to storage array controller 110A or storage arraycontroller 110B. Storage array controller 101 includes numerous elementsfor purposes of illustration rather than limitation. It may be notedthat storage array controller 101 may include the same, more, or fewerelements configured in the same or different manner in otherimplementations. It may be noted that elements of FIG. 1A may beincluded below to help illustrate features of storage array controller101.

Storage array controller 101 may include one or more processing devices104 and random access memory (‘RAM’) 111. Processing device 104 (orcontroller 101) represents one or more general-purpose processingdevices such as a microprocessor, central processing unit, or the like.More particularly, the processing device 104 (or controller 101) may bea complex instruction set computing (‘CISC’) microprocessor, reducedinstruction set computing (‘RISC’) microprocessor, very long instructionword (‘VLIW’) microprocessor, or a processor implementing otherinstruction sets or processors implementing a combination of instructionsets. The processing device 104 (or controller 101) may also be one ormore special-purpose processing devices such as an application specificintegrated circuit (‘ASIC’), a field programmable gate array (‘FPGA’), adigital signal processor (‘DSP’), network processor, or the like.

The processing device 104 may be connected to the RAM 111 via a datacommunications link 106, which may be embodied as a high speed memorybus such as a Double-Data Rate 4 (‘DDR4’) bus. Stored in RAM 111 is anoperating system 112. In some implementations, instructions 113 arestored in RAM 111. Instructions 113 may include computer programinstructions for performing operations in a direct-mapped flash storagesystem. In one embodiment, a direct-mapped flash storage system is onethat addresses data blocks within flash drives directly and without anaddress translation performed by the storage controllers of the flashdrives.

In implementations, storage array controller 101 includes one or morehost bus adapters 103A-C that are coupled to the processing device 104via a data communications link 105A-C. In implementations, host busadapters 103A-C may be computer hardware that connects a host system(e.g., the storage array controller) to other network and storagearrays. In some examples, host bus adapters 103A-C may be a FibreChannel adapter that enables the storage array controller 101 to connectto a SAN, an Ethernet adapter that enables the storage array controller101 to connect to a LAN, or the like. Host bus adapters 103A-C may becoupled to the processing device 104 via a data communications link105A-C such as, for example, a PCIe bus.

In implementations, storage array controller 101 may include a host busadapter 114 that is coupled to an expander 115. The expander 115 may beused to attach a host system to a larger number of storage drives. Theexpander 115 may, for example, be a SAS expander utilized to enable thehost bus adapter 114 to attach to storage drives in an implementationwhere the host bus adapter 114 is embodied as a SAS controller.

In implementations, storage array controller 101 may include a switch116 coupled to the processing device 104 via a data communications link109. The switch 116 may be a computer hardware device that can createmultiple endpoints out of a single endpoint, thereby enabling multipledevices to share a single endpoint. The switch 116 may, for example, bea PCIe switch that is coupled to a PCIe bus (e.g., data communicationslink 109) and presents multiple PCIe connection points to the midplane.

In implementations, storage array controller 101 includes a datacommunications link 107 for coupling the storage array controller 101 toother storage array controllers. In some examples, data communicationslink 107 may be a QuickPath Interconnect (QPI) interconnect.

A traditional storage system that uses traditional flash drives mayimplement a process across the flash drives that are part of thetraditional storage system. For example, a higher level process of thestorage system may initiate and control a process across the flashdrives. However, a flash drive of the traditional storage system mayinclude its own storage controller that also performs the process. Thus,for the traditional storage system, a higher level process (e.g.,initiated by the storage system) and a lower level process (e.g.,initiated by a storage controller of the storage system) may both beperformed.

To resolve various deficiencies of a traditional storage system,operations may be performed by higher level processes and not by thelower level processes. For example, the flash storage system may includeflash drives that do not include storage controllers that provide theprocess. Thus, the operating system of the flash storage system itselfmay initiate and control the process. This may be accomplished by adirect-mapped flash storage system that addresses data blocks within theflash drives directly and without an address translation performed bythe storage controllers of the flash drives.

The operating system of the flash storage system may identify andmaintain a list of allocation units across multiple flash drives of theflash storage system. The allocation units may be entire erase blocks ormultiple erase blocks. The operating system may maintain a map oraddress range that directly maps addresses to erase blocks of the flashdrives of the flash storage system.

Direct mapping to the erase blocks of the flash drives may be used torewrite data and erase data. For example, the operations may beperformed on one or more allocation units that include a first data anda second data where the first data is to be retained and the second datais no longer being used by the flash storage system. The operatingsystem may initiate the process to write the first data to new locationswithin other allocation units and erasing the second data and markingthe allocation units as being available for use for subsequent data.Thus, the process may only be performed by the higher level operatingsystem of the flash storage system without an additional lower levelprocess being performed by controllers of the flash drives.

Advantages of the process being performed only by the operating systemof the flash storage system include increased reliability of the flashdrives of the flash storage system as unnecessary or redundant writeoperations are not being performed during the process. One possiblepoint of novelty here is the concept of initiating and controlling theprocess at the operating system of the flash storage system. Inaddition, the process can be controlled by the operating system acrossmultiple flash drives. This is in contrast to the process beingperformed by a storage controller of a flash drive.

A storage system can consist of two storage array controllers that sharea set of drives for failover purposes, or it could consist of a singlestorage array controller that provides a storage service that utilizesmultiple drives, or it could consist of a distributed network of storagearray controllers each with some number of drives or some amount ofFlash storage where the storage array controllers in the networkcollaborate to provide a complete storage service and collaborate onvarious aspects of a storage service including storage allocation andgarbage collection.

FIG. 1C illustrates a third example system 117 for data storage inaccordance with some implementations. System 117 (also referred to as“storage system” herein) includes numerous elements for purposes ofillustration rather than limitation. It may be noted that system 117 mayinclude the same, more, or fewer elements configured in the same ordifferent manner in other implementations.

In one embodiment, system 117 includes a dual Peripheral ComponentInterconnect (‘PCI’) flash storage device 118 with separatelyaddressable fast write storage. System 117 may include a storagecontroller 119. In one embodiment, storage controller 119 may be a CPU,ASIC, FPGA, or any other circuitry that may implement control structuresnecessary according to the present disclosure. In one embodiment, system117 includes flash memory devices (e.g., including flash memory devices120 a-n), operatively coupled to various channels of the storage devicecontroller 119. Flash memory devices 120 a-n, may be presented to thecontroller 119 as an addressable collection of Flash pages, eraseblocks, and/or control elements sufficient to allow the storage devicecontroller 119 to program and retrieve various aspects of the Flash. Inone embodiment, storage device controller 119 may perform operations onflash memory devices 120A-N including storing and retrieving datacontent of pages, arranging and erasing any blocks, tracking statisticsrelated to the use and reuse of Flash memory pages, erase blocks, andcells, tracking and predicting error codes and faults within the Flashmemory, controlling voltage levels associated with programming andretrieving contents of Flash cells, etc.

In one embodiment, system 117 may include RAM 121 to store separatelyaddressable fast-write data. In one embodiment, RAM 121 may be one ormore separate discrete devices. In another embodiment, RAM 121 may beintegrated into storage device controller 119 or multiple storage devicecontrollers. The RAM 121 may be utilized for other purposes as well,such as temporary program memory for a processing device (e.g., a CPU)in the storage device controller 119.

In one embodiment, system 119 may include a stored energy device 122,such as a rechargeable battery or a capacitor. Stored energy device 122may store energy sufficient to power the storage device controller 119,some amount of the RAM (e.g., RAM 121), and some amount of Flash memory(e.g., Flash memory 120 a-120 n) for sufficient time to write thecontents of RAM to Flash memory. In one embodiment, storage devicecontroller 119 may write the contents of RAM to Flash Memory if thestorage device controller detects loss of external power.

In one embodiment, system 117 includes two data communications links 123a, 123 b. In one embodiment, data communications links 123 a, 123 b maybe PCI interfaces. In another embodiment, data communications links 123a, 123 b may be based on other communications standards (e.g.,HyperTransport, InfiniBand, etc.). Data communications links 123 a, 123b may be based on non-volatile memory express (‘NVMe’) or NVMe overfabrics (‘NVMf’) specifications that allow external connection to thestorage device controller 119 from other components in the storagesystem 117. It should be noted that data communications links may beinterchangeably referred to herein as PCI buses for convenience.

System 117 may also include an external power source (not shown), whichmay be provided over one or both data communications links 123 a, 123 b,or which may be provided separately. An alternative embodiment includesa separate Flash memory (not shown) dedicated for use in storing thecontent of RAM 121. The storage device controller 119 may present alogical device over a PCI bus which may include an addressablefast-write logical device, or a distinct part of the logical addressspace of the storage device 118, which may be presented as PCI memory oras persistent storage. In one embodiment, operations to store into thedevice are directed into the RAM 121. On power failure, the storagedevice controller 119 may write stored content associated with theaddressable fast-write logical storage to Flash memory (e.g., Flashmemory 120 a-n) for long-term persistent storage.

In one embodiment, the logical device may include some presentation ofsome or all of the content of the Flash memory devices 120 a-n, wherethat presentation allows a storage system including a storage device 118(e.g., storage system 117) to directly address Flash memory pages anddirectly reprogram erase blocks from storage system components that areexternal to the storage device through the PCI bus. The presentation mayalso allow one or more of the external components to control andretrieve other aspects of the Flash memory including some or all of:tracking statistics related to use and reuse of Flash memory pages,erase blocks, and cells across all the Flash memory devices; trackingand predicting error codes and faults within and across the Flash memorydevices; controlling voltage levels associated with programming andretrieving contents of Flash cells; etc.

In one embodiment, the stored energy device 122 may be sufficient toensure completion of in-progress operations to the Flash memory devices107 a-120 n stored energy device 122 may power storage device controller119 and associated Flash memory devices (e.g., 120 a-n) for thoseoperations, as well as for the storing of fast-write RAM to Flashmemory. Stored energy device 122 may be used to store accumulatedstatistics and other parameters kept and tracked by the Flash memorydevices 120 a-n and/or the storage device controller 119. Separatecapacitors or stored energy devices (such as smaller capacitors near orembedded within the Flash memory devices themselves) may be used forsome or all of the operations described herein.

Various schemes may be used to track and optimize the life span of thestored energy component, such as adjusting voltage levels over time,partially discharging the storage energy device 122 to measurecorresponding discharge characteristics, etc. If the available energydecreases over time, the effective available capacity of the addressablefast-write storage may be decreased to ensure that it can be writtensafely based on the currently available stored energy.

FIG. 1D illustrates a third example system 124 for data storage inaccordance with some implementations. In one embodiment, system 124includes storage controllers 125 a, 125 b. In one embodiment, storagecontrollers 125 a, 125 b are operatively coupled to Dual PCI storagedevices 119 a, 119 b and 119 c, 119 d, respectively. Storage controllers125 a, 125 b may be operatively coupled (e.g., via a storage network130) to some number of host computers 127 a-n.

In one embodiment, two storage controllers (e.g., 125 a and 125 b)provide storage services, such as a SCS block storage array, a fileserver, an object server, a database or data analytics service, etc. Thestorage controllers 125 a, 125 b may provide services through somenumber of network interfaces (e.g., 126 a-d) to host computers 127 a-noutside of the storage system 124. Storage controllers 125 a, 125 b mayprovide integrated services or an application entirely within thestorage system 124, forming a converged storage and compute system. Thestorage controllers 125 a, 125 b may utilize the fast write memorywithin or across storage devices 119 a-d to journal in progressoperations to ensure the operations are not lost on a power failure,storage controller removal, storage controller or storage systemshutdown, or some fault of one or more software or hardware componentswithin the storage system 124.

In one embodiment, controllers 125 a, 125 b operate as PCI masters toone or the other PCI buses 128 a, 128 b. In another embodiment, 128 aand 128 b may be based on other communications standards (e.g.,HyperTransport, InfiniBand, etc.). Other storage system embodiments mayoperate storage controllers 125 a, 125 b as multi-masters for both PCIbuses 128 a, 128 b. Alternately, a PCI/NVMe/NVMf switchinginfrastructure or fabric may connect multiple storage controllers. Somestorage system embodiments may allow storage devices to communicate witheach other directly rather than communicating only with storagecontrollers. In one embodiment, a storage device controller 119 a may beoperable under direction from a storage controller 125 a to synthesizeand transfer data to be stored into Flash memory devices from data thathas been stored in RAM (e.g., RAM 121 of FIG. 1C). For example, arecalculated version of RAM content may be transferred after a storagecontroller has determined that an operation has fully committed acrossthe storage system, or when fast-write memory on the device has reacheda certain used capacity, or after a certain amount of time, to ensureimprove safety of the data or to release addressable fast-write capacityfor reuse. This mechanism may be used, for example, to avoid a secondtransfer over a bus (e.g., 128 a, 128 b) from the storage controllers125 a, 125 b. In one embodiment, a recalculation may include compressingdata, attaching indexing or other metadata, combining multiple datasegments together, performing erasure code calculations, etc.

In one embodiment, under direction from a storage controller 125 a, 125b, a storage device controller 119 a, 119 b may be operable to calculateand transfer data to other storage devices from data stored in RAM(e.g., RAM 121 of FIG. 1C) without involvement of the storagecontrollers 125 a, 125 b. This operation may be used to mirror datastored in one controller 125 a to another controller 125 b, or it couldbe used to offload compression, data aggregation, and/or erasure codingcalculations and transfers to storage devices to reduce load on storagecontrollers or the storage controller interface 129 a, 129 b to the PCIbus 128 a, 128 b.

A storage device controller 119 may include mechanisms for implementinghigh availability primitives for use by other parts of a storage systemexternal to the Dual PCI storage device 118. For example, reservation orexclusion primitives may be provided so that, in a storage system withtwo storage controllers providing a highly available storage service,one storage controller may prevent the other storage controller fromaccessing or continuing to access the storage device. This could beused, for example, in cases where one controller detects that the othercontroller is not functioning properly or where the interconnect betweenthe two storage controllers may itself not be functioning properly.

In one embodiment, a storage system for use with Dual PCI direct mappedstorage devices with separately addressable fast write storage includessystems that manage erase blocks or groups of erase blocks as allocationunits for storing data on behalf of the storage service, or for storingmetadata (e.g., indexes, logs, etc.) associated with the storageservice, or for proper management of the storage system itself. Flashpages, which may be a few kilobytes in size, may be written as dataarrives or as the storage system is to persist data for long intervalsof time (e.g., above a defined threshold of time). To commit data morequickly, or to reduce the number of writes to the Flash memory devices,the storage controllers may first write data into the separatelyaddressable fast write storage on one or more storage devices.

In one embodiment, the storage controllers 125 a, 125 b may initiate theuse of erase blocks within and across storage devices (e.g., 118) inaccordance with an age and expected remaining lifespan of the storagedevices, or based on other statistics. The storage controllers 125 a,125 b may initiate garbage collection and data migration data betweenstorage devices in accordance with pages that are no longer needed aswell as to manage Flash page and erase block lifespans and to manageoverall system performance.

In one embodiment, the storage system 124 may utilize mirroring and/orerasure coding schemes as part of storing data into addressable fastwrite storage and/or as part of writing data into allocation unitsassociated with erase blocks. Erasure codes may be used across storagedevices, as well as within erase blocks or allocation units, or withinand across Flash memory devices on a single storage device, to provideredundancy against single or multiple storage device failures or toprotect against internal corruptions of Flash memory pages resultingfrom Flash memory operations or from degradation of Flash memory cells.Mirroring and erasure coding at various levels may be used to recoverfrom multiple types of failures that occur separately or in combination.

The embodiments depicted with reference to FIGS. 2A-G illustrate astorage cluster that stores user data, such as user data originatingfrom one or more user or client systems or other sources external to thestorage cluster. The storage cluster distributes user data acrossstorage nodes housed within a chassis, or across multiple chassis, usingerasure coding and redundant copies of metadata. Erasure coding refersto a method of data protection or reconstruction in which data is storedacross a set of different locations, such as disks, storage nodes orgeographic locations. Flash memory is one type of solid-state memorythat may be integrated with the embodiments, although the embodimentsmay be extended to other types of solid-state memory or other storagemedium, including non- solid state memory. Control of storage locationsand workloads are distributed across the storage locations in aclustered peer-to-peer system. Tasks such as mediating communicationsbetween the various storage nodes, detecting when a storage node hasbecome unavailable, and balancing I/Os (inputs and outputs) across thevarious storage nodes, are all handled on a distributed basis. Data islaid out or distributed across multiple storage nodes in data fragmentsor stripes that support data recovery in some embodiments. Ownership ofdata can be reassigned within a cluster, independent of input and outputpatterns. This architecture described in more detail below allows astorage node in the cluster to fail, with the system remainingoperational, since the data can be reconstructed from other storagenodes and thus remain available for input and output operations. Invarious embodiments, a storage node may be referred to as a clusternode, a blade, or a server.

The storage cluster may be contained within a chassis, i.e., anenclosure housing one or more storage nodes. A mechanism to providepower to each storage node, such as a power distribution bus, and acommunication mechanism, such as a communication bus that enablescommunication between the storage nodes are included within the chassis.The storage cluster can run as an independent system in one locationaccording to some embodiments. In one embodiment, a chassis contains atleast two instances of both the power distribution and the communicationbus which may be enabled or disabled independently. The internalcommunication bus may be an Ethernet bus, however, other technologiessuch as PCIe, InfiniBand, and others, are equally suitable. The chassisprovides a port for an external communication bus for enablingcommunication between multiple chassis, directly or through a switch,and with client systems. The external communication may use a technologysuch as Ethernet, InfiniBand, Fibre Channel, etc. In some embodiments,the external communication bus uses different communication bustechnologies for inter-chassis and client communication. If a switch isdeployed within or between chassis, the switch may act as a translationbetween multiple protocols or technologies. When multiple chassis areconnected to define a storage cluster, the storage cluster may beaccessed by a client using either proprietary interfaces or standardinterfaces such as network file system (‘NFS’), common internet filesystem (‘CIFS’), small computer system interface (‘SCSI’) or hypertexttransfer protocol (‘HTTP’). Translation from the client protocol mayoccur at the switch, chassis external communication bus or within eachstorage node. In some embodiments, multiple chassis may be coupled orconnected to each other through an aggregator switch. A portion and/orall of the coupled or connected chassis may be designated as a storagecluster. As discussed above, each chassis can have multiple blades, eachblade has a media access control (‘MAC’) address, but the storagecluster is presented to an external network as having a single clusterIP address and a single MAC address in some embodiments.

Each storage node may be one or more storage servers and each storageserver is connected to one or more non-volatile solid state memoryunits, which may be referred to as storage units or storage devices. Oneembodiment includes a single storage server in each storage node andbetween one to eight non-volatile solid state memory units, however thisone example is not meant to be limiting. The storage server may includea processor, DRAM and interfaces for the internal communication bus andpower distribution for each of the power buses. Inside the storage node,the interfaces and storage unit share a communication bus, e.g., PCIExpress, in some embodiments. The non-volatile solid state memory unitsmay directly access the internal communication bus interface through astorage node communication bus, or request the storage node to accessthe bus interface. The non-volatile solid state memory unit contains anembedded CPU, solid state storage controller, and a quantity of solidstate mass storage, e.g., between 2-32 terabytes (‘TB’) in someembodiments. An embedded volatile storage medium, such as DRAM, and anenergy reserve apparatus are included in the non-volatile solid statememory unit. In some embodiments, the energy reserve apparatus is acapacitor, super-capacitor, or battery that enables transferring asubset of DRAM contents to a stable storage medium in the case of powerloss. In some embodiments, the non-volatile solid state memory unit isconstructed with a storage class memory, such as phase change ormagnetoresistive random access memory (‘MRAM’) that substitutes for DRAMand enables a reduced power hold-up apparatus.

One of many features of the storage nodes and non-volatile solid statestorage is the ability to proactively rebuild data in a storage cluster.The storage nodes and non-volatile solid state storage can determinewhen a storage node or non-volatile solid state storage in the storagecluster is unreachable, independent of whether there is an attempt toread data involving that storage node or non-volatile solid statestorage. The storage nodes and non-volatile solid state storage thencooperate to recover and rebuild the data in at least partially newlocations. This constitutes a proactive rebuild, in that the systemrebuilds data without waiting until the data is needed for a read accessinitiated from a client system employing the storage cluster. These andfurther details of the storage memory and operation thereof arediscussed below.

FIG. 2A is a perspective view of a storage cluster 161, with multiplestorage nodes 150 and internal solid-state memory coupled to eachstorage node to provide network attached storage or storage areanetwork, in accordance with some embodiments. A network attachedstorage, storage area network, or a storage cluster, or other storagememory, could include one or more storage clusters 161, each having oneor more storage nodes 150, in a flexible and reconfigurable arrangementof both the physical components and the amount of storage memoryprovided thereby. The storage cluster 161 is designed to fit in a rack,and one or more racks can be set up and populated as desired for thestorage memory. The storage cluster 161 has a chassis 138 havingmultiple slots 142. It should be appreciated that chassis 138 may bereferred to as a housing, enclosure, or rack unit. In one embodiment,the chassis 138 has fourteen slots 142, although other numbers of slotsare readily devised. For example, some embodiments have four slots,eight slots, sixteen slots, thirty-two slots, or other suitable numberof slots. Each slot 142 can accommodate one storage node 150 in someembodiments. Chassis 138 includes flaps 148 that can be utilized tomount the chassis 138 on a rack. Fans 144 provide air circulation forcooling of the storage nodes 150 and components thereof, although othercooling components could be used, or an embodiment could be devisedwithout cooling components. A switch fabric 146 couples storage nodes150 within chassis 138 together and to a network for communication tothe memory. In an embodiment depicted in herein, the slots 142 to theleft of the switch fabric 146 and fans 144 are shown occupied by storagenodes 150, while the slots 142 to the right of the switch fabric 146 andfans 144 are empty and available for insertion of storage node 150 forillustrative purposes. This configuration is one example, and one ormore storage nodes 150 could occupy the slots 142 in various furtherarrangements. The storage node arrangements need not be sequential oradjacent in some embodiments. Storage nodes 150 are hot pluggable,meaning that a storage node 150 can be inserted into a slot 142 in thechassis 138, or removed from a slot 142, without stopping or poweringdown the system. Upon insertion or removal of storage node 150 from slot142, the system automatically reconfigures in order to recognize andadapt to the change. Reconfiguration, in some embodiments, includesrestoring redundancy and/or rebalancing data or load.

Each storage node 150 can have multiple components. In the embodimentshown here, the storage node 150 includes a printed circuit board 159populated by a CPU 156, i.e., processor, a memory 154 coupled to the CPU156, and a non-volatile solid state storage 152 coupled to the CPU 156,although other mountings and/or components could be used in furtherembodiments. The memory 154 has instructions which are executed by theCPU 156 and/or data operated on by the CPU 156. As further explainedbelow, the non-volatile solid state storage 152 includes flash or, infurther embodiments, other types of solid-state memory.

Referring to FIG. 2A, storage cluster 161 is scalable, meaning thatstorage capacity with non-uniform storage sizes is readily added, asdescribed above. One or more storage nodes 150 can be plugged into orremoved from each chassis and the storage cluster self-configures insome embodiments. Plug-in storage nodes 150, whether installed in achassis as delivered or later added, can have different sizes. Forexample, in one embodiment a storage node 150 can have any multiple of 4TB, e.g., 8 TB, 12 TB, 16 TB, 32 TB, etc. In further embodiments, astorage node 150 could have any multiple of other storage amounts orcapacities. Storage capacity of each storage node 150 is broadcast, andinfluences decisions of how to stripe the data. For maximum storageefficiency, an embodiment can self-configure as wide as possible in thestripe, subject to a predetermined requirement of continued operationwith loss of up to one, or up to two, non-volatile solid state storageunits 152 or storage nodes 150 within the chassis.

FIG. 2B is a block diagram showing a communications interconnect 171A-Fand power distribution bus 172 coupling multiple storage nodes 150.Referring back to FIG. 2A, the communications interconnect 171A-F can beincluded in or implemented with the switch fabric 146 in someembodiments. Where multiple storage clusters 161 occupy a rack, thecommunications interconnect 171A-F can be included in or implementedwith a top of rack switch, in some embodiments. As illustrated in FIG.2B, storage cluster 161 is enclosed within a single chassis 138.External port 176 is coupled to storage nodes 150 through communicationsinterconnect 171A-F, while external port 174 is coupled directly to astorage node. External power port 178 is coupled to power distributionbus 172. Storage nodes 150 may include varying amounts and differingcapacities of non-volatile solid state storage 152 as described withreference to FIG. 2A. In addition, one or more storage nodes 150 may bea compute only storage node as illustrated in FIG. 2B. Authorities 168are implemented on the non-volatile solid state storages 152, forexample as lists or other data structures stored in memory. In someembodiments the authorities are stored within the non-volatile solidstate storage 152 and supported by software executing on a controller orother processor of the non-volatile solid state storage 152. In afurther embodiment, authorities 168 are implemented on the storage nodes150, for example as lists or other data structures stored in the memory154 and supported by software executing on the CPU 156 of the storagenode 150. Authorities 168 control how and where data is stored in thenon-volatile solid state storages 152 in some embodiments. This controlassists in determining which type of erasure coding scheme is applied tothe data, and which storage nodes 150 have which portions of the data.Each authority 168 may be assigned to a non-volatile solid state storage152. Each authority may control a range of inode numbers, segmentnumbers, or other data identifiers which are assigned to data by a filesystem, by the storage nodes 150, or by the non-volatile solid statestorage 152, in various embodiments.

Every piece of data, and every piece of metadata, has redundancy in thesystem in some embodiments. In addition, every piece of data and everypiece of metadata has an owner, which may be referred to as anauthority. If that authority is unreachable, for example through failureof a storage node, there is a plan of succession for how to find thatdata or that metadata. In various embodiments, there are redundantcopies of authorities 168. Authorities 168 have a relationship tostorage nodes 150 and non-volatile solid state storage 152 in someembodiments. Each authority 168, covering a range of data segmentnumbers or other identifiers of the data, may be assigned to a specificnon-volatile solid state storage 152. In some embodiments theauthorities 168 for all of such ranges are distributed over thenon-volatile solid state storages 152 of a storage cluster. Each storagenode 150 has a network port that provides access to the non-volatilesolid state storage(s) 152 of that storage node 150. Data can be storedin a segment, which is associated with a segment number and that segmentnumber is an indirection for a configuration of a RAID (redundant arrayof independent disks) stripe in some embodiments. The assignment and useof the authorities 168 thus establishes an indirection to data.Indirection may be referred to as the ability to reference dataindirectly, in this case via an authority 168, in accordance with someembodiments. A segment identifies a set of non-volatile solid statestorage 152 and a local identifier into the set of non-volatile solidstate storage 152 that may contain data. In some embodiments, the localidentifier is an offset into the device and may be reused sequentiallyby multiple segments. In other embodiments the local identifier isunique for a specific segment and never reused. The offsets in thenon-volatile solid state storage 152 are applied to locating data forwriting to or reading from the non-volatile solid state storage 152 (inthe form of a RAID stripe). Data is striped across multiple units ofnon-volatile solid state storage 152, which may include or be differentfrom the non-volatile solid state storage 152 having the authority 168for a particular data segment.

If there is a change in where a particular segment of data is located,e.g., during a data move or a data reconstruction, the authority 168 forthat data segment should be consulted, at that non-volatile solid statestorage 152 or storage node 150 having that authority 168. In order tolocate a particular piece of data, embodiments calculate a hash valuefor a data segment or apply an inode number or a data segment number.The output of this operation points to a non-volatile solid statestorage 152 having the authority 168 for that particular piece of data.In some embodiments there are two stages to this operation. The firststage maps an entity identifier (ID), e.g., a segment number, inodenumber, or directory number to an authority identifier. This mapping mayinclude a calculation such as a hash or a bit mask. The second stage ismapping the authority identifier to a particular non-volatile solidstate storage 152, which may be done through an explicit mapping. Theoperation is repeatable, so that when the calculation is performed, theresult of the calculation repeatably and reliably points to a particularnon-volatile solid state storage 152 having that authority 168. Theoperation may include the set of reachable storage nodes as input. Ifthe set of reachable non-volatile solid state storage units changes theoptimal set changes. In some embodiments, the persisted value is thecurrent assignment (which is always true) and the calculated value isthe target assignment the cluster will attempt to reconfigure towards.This calculation may be used to determine the optimal non-volatile solidstate storage 152 for an authority in the presence of a set ofnon-volatile solid state storage 152 that are reachable and constitutethe same cluster. The calculation also determines an ordered set of peernon-volatile solid state storage 152 that will also record the authorityto non-volatile solid state storage mapping so that the authority may bedetermined even if the assigned non-volatile solid state storage isunreachable. A duplicate or substitute authority 168 may be consulted ifa specific authority 168 is unavailable in some embodiments.

With reference to FIGS. 2A and 2B, two of the many tasks of the CPU 156on a storage node 150 are to break up write data, and reassemble readdata. When the system has determined that data is to be written, theauthority 168 for that data is located as above. When the segment ID fordata is already determined the request to write is forwarded to thenon-volatile solid state storage 152 currently determined to be the hostof the authority 168 determined from the segment. The host CPU 156 ofthe storage node 150, on which the non-volatile solid state storage 152and corresponding authority 168 reside, then breaks up or shards thedata and transmits the data out to various non-volatile solid statestorage 152. The transmitted data is written as a data stripe inaccordance with an erasure coding scheme. In some embodiments, data isrequested to be pulled, and in other embodiments, data is pushed. Inreverse, when data is read, the authority 168 for the segment IDcontaining the data is located as described above. The host CPU 156 ofthe storage node 150 on which the non-volatile solid state storage 152and corresponding authority 168 reside requests the data from thenon-volatile solid state storage and corresponding storage nodes pointedto by the authority. In some embodiments the data is read from flashstorage as a data stripe. The host CPU 156 of storage node 150 thenreassembles the read data, correcting any errors (if present) accordingto the appropriate erasure coding scheme, and forwards the reassembleddata to the network. In further embodiments, some or all of these taskscan be handled in the non-volatile solid state storage 152. In someembodiments, the segment host requests the data be sent to storage node150 by requesting pages from storage and then sending the data to thestorage node making the original request.

In some systems, for example in UNIX-style file systems, data is handledwith an index node or inode, which specifies a data structure thatrepresents an object in a file system. The object could be a file or adirectory, for example. Metadata may accompany the object, as attributessuch as permission data and a creation timestamp, among otherattributes. A segment number could be assigned to all or a portion ofsuch an object in a file system. In other systems, data segments arehandled with a segment number assigned elsewhere. For purposes ofdiscussion, the unit of distribution is an entity, and an entity can bea file, a directory or a segment. That is, entities are units of data ormetadata stored by a storage system. Entities are grouped into setscalled authorities. Each authority has an authority owner, which is astorage node that has the exclusive right to update the entities in theauthority. In other words, a storage node contains the authority, andthat the authority, in turn, contains entities.

A segment is a logical container of data in accordance with someembodiments. A segment is an address space between medium address spaceand physical flash locations, i.e., the data segment number, are in thisaddress space. Segments may also contain meta-data, which enable dataredundancy to be restored (rewritten to different flash locations ordevices) without the involvement of higher level software. In oneembodiment, an internal format of a segment contains client data andmedium mappings to determine the position of that data. Each datasegment is protected, e.g., from memory and other failures, by breakingthe segment into a number of data and parity shards, where applicable.The data and parity shards are distributed, i.e., striped, acrossnon-volatile solid state storage 152 coupled to the host CPUs 156 (SeeFIGS. 2E and 2G) in accordance with an erasure coding scheme. Usage ofthe term segments refers to the container and its place in the addressspace of segments in some embodiments. Usage of the term stripe refersto the same set of shards as a segment and includes how the shards aredistributed along with redundancy or parity information in accordancewith some embodiments.

A series of address-space transformations takes place across an entirestorage system. At the top are the directory entries (file names) whichlink to an inode. Inodes point into medium address space, where data islogically stored. Medium addresses may be mapped through a series ofindirect mediums to spread the load of large files, or implement dataservices like deduplication or snapshots. Segment addresses are thentranslated into physical flash locations. Physical flash locations havean address range bounded by the amount of flash in the system inaccordance with some embodiments. Medium addresses and segment addressesare logical containers, and in some embodiments use a 128 bit or largeridentifier so as to be practically infinite, with a likelihood of reusecalculated as longer than the expected life of the system. Addressesfrom logical containers are allocated in a hierarchical fashion in someembodiments. Initially, each non-volatile solid state storage unit 152may be assigned a range of address space. Within this assigned range,the non-volatile solid state storage 152 is able to allocate addresseswithout synchronization with other non-volatile solid state storage 152.

Data and metadata is stored by a set of underlying storage layouts thatare optimized for varying workload patterns and storage devices. Theselayouts incorporate multiple redundancy schemes, compression formats andindex algorithms. Some of these layouts store information aboutauthorities and authority masters, while others store file metadata andfile data. The redundancy schemes include error correction codes thattolerate corrupted bits within a single storage device (such as a NANDflash chip), erasure codes that tolerate the failure of multiple storagenodes, and replication schemes that tolerate data center or regionalfailures. In some embodiments, low density parity check (‘LDPC’) code isused within a single storage unit. Reed-Solomon encoding is used withina storage cluster, and mirroring is used within a storage grid in someembodiments. Metadata may be stored using an ordered log structuredindex (such as a Log Structured Merge Tree), and large data may not bestored in a log structured layout.

In order to maintain consistency across multiple copies of an entity,the storage nodes agree implicitly on two things through calculations:(1) the authority that contains the entity, and (2) the storage nodethat contains the authority. The assignment of entities to authoritiescan be done by pseudo randomly assigning entities to authorities, bysplitting entities into ranges based upon an externally produced key, orby placing a single entity into each authority. Examples of pseudorandomschemes are linear hashing and the Replication Under Scalable Hashing(‘RUSH’) family of hashes, including Controlled Replication UnderScalable Hashing (‘CRUSH’). In some embodiments, pseudo-randomassignment is utilized only for assigning authorities to nodes becausethe set of nodes can change. The set of authorities cannot change so anysubjective function may be applied in these embodiments. Some placementschemes automatically place authorities on storage nodes, while otherplacement schemes rely on an explicit mapping of authorities to storagenodes. In some embodiments, a pseudorandom scheme is utilized to mapfrom each authority to a set of candidate authority owners. Apseudorandom data distribution function related to CRUSH may assignauthorities to storage nodes and create a list of where the authoritiesare assigned. Each storage node has a copy of the pseudorandom datadistribution function, and can arrive at the same calculation fordistributing, and later finding or locating an authority. Each of thepseudorandom schemes requires the reachable set of storage nodes asinput in some embodiments in order to conclude the same target nodes.Once an entity has been placed in an authority, the entity may be storedon physical devices so that no expected failure will lead to unexpecteddata loss. In some embodiments, rebalancing algorithms attempt to storethe copies of all entities within an authority in the same layout and onthe same set of machines.

Examples of expected failures include device failures, stolen machines,datacenter fires, and regional disasters, such as nuclear or geologicalevents. Different failures lead to different levels of acceptable dataloss. In some embodiments, a stolen storage node impacts neither thesecurity nor the reliability of the system, while depending on systemconfiguration, a regional event could lead to no loss of data, a fewseconds or minutes of lost updates, or even complete data loss.

In the embodiments, the placement of data for storage redundancy isindependent of the placement of authorities for data consistency. Insome embodiments, storage nodes that contain authorities do not containany persistent storage. Instead, the storage nodes are connected tonon-volatile solid state storage units that do not contain authorities.The communications interconnect between storage nodes and non-volatilesolid state storage units consists of multiple communicationtechnologies and has non-uniform performance and fault tolerancecharacteristics. In some embodiments, as mentioned above, non-volatilesolid state storage units are connected to storage nodes via PCIexpress, storage nodes are connected together within a single chassisusing Ethernet backplane, and chassis are connected together to form astorage cluster. Storage clusters are connected to clients usingEthernet or fiber channel in some embodiments. If multiple storageclusters are configured into a storage grid, the multiple storageclusters are connected using the Internet or other long-distancenetworking links, such as a “metro scale” link or private link that doesnot traverse the internet.

Authority owners have the exclusive right to modify entities, to migrateentities from one non-volatile solid state storage unit to anothernon-volatile solid state storage unit, and to add and remove copies ofentities. This allows for maintaining the redundancy of the underlyingdata. When an authority owner fails, is going to be decommissioned, oris overloaded, the authority is transferred to a new storage node.Transient failures make it non-trivial to ensure that all non-faultymachines agree upon the new authority location. The ambiguity thatarises due to transient failures can be achieved automatically by aconsensus protocol such as Paxos, hot-warm failover schemes, via manualintervention by a remote system administrator, or by a local hardwareadministrator (such as by physically removing the failed machine fromthe cluster, or pressing a button on the failed machine). In someembodiments, a consensus protocol is used, and failover is automatic. Iftoo many failures or replication events occur in too short a timeperiod, the system goes into a self-preservation mode and haltsreplication and data movement activities until an administratorintervenes in accordance with some embodiments.

As authorities are transferred between storage nodes and authorityowners update entities in their authorities, the system transfersmessages between the storage nodes and non-volatile solid state storageunits. With regard to persistent messages, messages that have differentpurposes are of different types. Depending on the type of the message,the system maintains different ordering and durability guarantees. Asthe persistent messages are being processed, the messages aretemporarily stored in multiple durable and non-durable storage hardwaretechnologies. In some embodiments, messages are stored in RAM, NVRAM andon NAND flash devices, and a variety of protocols are used in order tomake efficient use of each storage medium. Latency-sensitive clientrequests may be persisted in replicated NVRAM, and then later NAND,while background rebalancing operations are persisted directly to NAND.

Persistent messages are persistently stored prior to being transmitted.This allows the system to continue to serve client requests despitefailures and component replacement. Although many hardware componentscontain unique identifiers that are visible to system administrators,manufacturer, hardware supply chain and ongoing monitoring qualitycontrol infrastructure, applications running on top of theinfrastructure address virtualize addresses. These virtualized addressesdo not change over the lifetime of the storage system, regardless ofcomponent failures and replacements. This allows each component of thestorage system to be replaced over time without reconfiguration ordisruptions of client request processing, i.e., the system supportsnon-disruptive upgrades.

In some embodiments, the virtualized addresses are stored withsufficient redundancy. A continuous monitoring system correlateshardware and software status and the hardware identifiers. This allowsdetection and prediction of failures due to faulty components andmanufacturing details. The monitoring system also enables the proactivetransfer of authorities and entities away from impacted devices beforefailure occurs by removing the component from the critical path in someembodiments.

FIG. 2C is a multiple level block diagram, showing contents of a storagenode 150 and contents of a non-volatile solid state storage 152 of thestorage node 150. Data is communicated to and from the storage node 150by a network interface controller (‘NIC’) 202 in some embodiments. Eachstorage node 150 has a CPU 156, and one or more non-volatile solid statestorage 152, as discussed above. Moving down one level in FIG. 2C, eachnon-volatile solid state storage 152 has a relatively fast non-volatilesolid state memory, such as nonvolatile random access memory (‘NVRAM’)204, and flash memory 206. In some embodiments, NVRAM 204 may be acomponent that does not require program/erase cycles (DRAM, MRAM, PCM),and can be a memory that can support being written vastly more oftenthan the memory is read from. Moving down another level in FIG. 2C, theNVRAM 204 is implemented in one embodiment as high speed volatilememory, such as dynamic random access memory (DRAM) 216, backed up byenergy reserve 218. Energy reserve 218 provides sufficient electricalpower to keep the DRAM 216 powered long enough for contents to betransferred to the flash memory 206 in the event of power failure. Insome embodiments, energy reserve 218 is a capacitor, super-capacitor,battery, or other device, that supplies a suitable supply of energysufficient to enable the transfer of the contents of DRAM 216 to astable storage medium in the case of power loss. The flash memory 206 isimplemented as multiple flash dies 222, which may be referred to aspackages of flash dies 222 or an array of flash dies 222. It should beappreciated that the flash dies 222 could be packaged in any number ofways, with a single die per package, multiple dies per package (i.e.multichip packages), in hybrid packages, as bare dies on a printedcircuit board or other substrate, as encapsulated dies, etc. In theembodiment shown, the non-volatile solid state storage 152 has acontroller 212 or other processor, and an input output (I/O) port 210coupled to the controller 212. I/O port 210 is coupled to the CPU 156and/or the network interface controller 202 of the flash storage node150. Flash input output (I/O) port 220 is coupled to the flash dies 222,and a direct memory access unit (DMA) 214 is coupled to the controller212, the DRAM 216 and the flash dies 222. In the embodiment shown, theI/O port 210, controller 212, DMA unit 214 and flash I/O port 220 areimplemented on a programmable logic device (‘PLD’) 208, e.g., a fieldprogrammable gate array (FPGA). In this embodiment, each flash die 222has pages, organized as sixteen kB (kilobyte) pages 224, and a register226 through which data can be written to or read from the flash die 222.In further embodiments, other types of solid-state memory are used inplace of, or in addition to flash memory illustrated within flash die222.

Storage clusters 161, in various embodiments as disclosed herein, can becontrasted with storage arrays in general. The storage nodes 150 arepart of a collection that creates the storage cluster 161. Each storagenode 150 owns a slice of data and computing required to provide thedata. Multiple storage nodes 150 cooperate to store and retrieve thedata. Storage memory or storage devices, as used in storage arrays ingeneral, are less involved with processing and manipulating the data.Storage memory or storage devices in a storage array receive commands toread, write, or erase data. The storage memory or storage devices in astorage array are not aware of a larger system in which they areembedded, or what the data means. Storage memory or storage devices instorage arrays can include various types of storage memory, such as RAM,solid state drives, hard disk drives, etc. The storage units 152described herein have multiple interfaces active simultaneously andserving multiple purposes. In some embodiments, some of thefunctionality of a storage node 150 is shifted into a storage unit 152,transforming the storage unit 152 into a combination of storage unit 152and storage node 150. Placing computing (relative to storage data) intothe storage unit 152 places this computing closer to the data itself.The various system embodiments have a hierarchy of storage node layerswith different capabilities. By contrast, in a storage array, acontroller owns and knows everything about all of the data that thecontroller manages in a shelf or storage devices. In a storage cluster161, as described herein, multiple controllers in multiple storage units152 and/or storage nodes 150 cooperate in various ways (e.g., forerasure coding, data sharding, metadata communication and redundancy,storage capacity expansion or contraction, data recovery, and so on).

FIG. 2D shows a storage server environment, which uses embodiments ofthe storage nodes 150 and storage units 152 of FIGS. 2A-C. In thisversion, each storage unit 152 has a processor such as controller 212(see FIG. 2C), an FPGA (field programmable gate array), flash memory206, and NVRAM 204 (which is super-capacitor backed DRAM 216, see FIGS.2B and 2C) on a PCIe (peripheral component interconnect express) boardin a chassis 138 (see FIG. 2A). The storage unit 152 may be implementedas a single board containing storage, and may be the largest tolerablefailure domain inside the chassis. In some embodiments, up to twostorage units 152 may fail and the device will continue with no dataloss.

The physical storage is divided into named regions based on applicationusage in some embodiments. The NVRAM 204 is a contiguous block ofreserved memory in the storage unit 152 DRAM 216, and is backed by NANDflash. NVRAM 204 is logically divided into multiple memory regionswritten for two as spool (e.g., spool_region). Space within the NVRAM204 spools is managed by each authority 168 independently. Each deviceprovides an amount of storage space to each authority 168. Thatauthority 168 further manages lifetimes and allocations within thatspace. Examples of a spool include distributed transactions or notions.When the primary power to a storage unit 152 fails, onboardsuper-capacitors provide a short duration of power hold up. During thisholdup interval, the contents of the NVRAM 204 are flushed to flashmemory 206. On the next power-on, the contents of the NVRAM 204 arerecovered from the flash memory 206.

As for the storage unit controller, the responsibility of the logical“controller” is distributed across each of the blades containingauthorities 168. This distribution of logical control is shown in FIG.2D as a host controller 242, mid-tier controller 244 and storage unitcontroller(s) 246. Management of the control plane and the storage planeare treated independently, although parts may be physically co-locatedon the same blade. Each authority 168 effectively serves as anindependent controller. Each authority 168 provides its own data andmetadata structures, its own background workers, and maintains its ownlifecycle.

FIG. 2E is a blade 252 hardware block diagram, showing a control plane254, compute and storage planes 256, 258, and authorities 168interacting with underlying physical resources, using embodiments of thestorage nodes 150 and storage units 152 of FIGS. 2A-C in the storageserver environment of FIG. 2D. The control plane 254 is partitioned intoa number of authorities 168 which can use the compute resources in thecompute plane 256 to run on any of the blades 252. The storage plane 258is partitioned into a set of devices, each of which provides access toflash 206 and NVRAM 204 resources.

In the compute and storage planes 256, 258 of FIG. 2E, the authorities168 interact with the underlying physical resources (i.e., devices).From the point of view of an authority 168, its resources are stripedover all of the physical devices. From the point of view of a device, itprovides resources to all authorities 168, irrespective of where theauthorities happen to run. Each authority 168 has allocated or has beenallocated one or more partitions 260 of storage memory in the storageunits 152, e.g. partitions 260 in flash memory 206 and NVRAM 204. Eachauthority 168 uses those allocated partitions 260 that belong to it, forwriting or reading user data. Authorities can be associated withdiffering amounts of physical storage of the system. For example, oneauthority 168 could have a larger number of partitions 260 or largersized partitions 260 in one or more storage units 152 than one or moreother authorities 168.

FIG. 2F depicts elasticity software layers in blades 252 of a storagecluster, in accordance with some embodiments. In the elasticitystructure, elasticity software is symmetric, i.e., each blade’s computemodule 270 runs the three identical layers of processes depicted in FIG.2F. Storage managers 274 execute read and write requests from otherblades 252 for data and metadata stored in local storage unit 152 NVRAM204 and flash 206. Authorities 168 fulfill client requests by issuingthe necessary reads and writes to the blades 252 on whose storage units152 the corresponding data or metadata resides. Endpoints 272 parseclient connection requests received from switch fabric 146 supervisorysoftware, relay the client connection requests to the authorities 168responsible for fulfillment, and relay the authorities′ 168 responses toclients. The symmetric three-layer structure enables the storagesystem’s high degree of concurrency. Elasticity scales out efficientlyand reliably in these embodiments. In addition, elasticity implements aunique scale-out technique that balances work evenly across allresources regardless of client access pattern, and maximizes concurrencyby eliminating much of the need for inter-blade coordination thattypically occurs with conventional distributed locking.

Still referring to FIG. 2F, authorities 168 running in the computemodules 270 of a blade 252 perform the internal operations required tofulfill client requests. One feature of elasticity is that authorities168 are stateless, i.e., they cache active data and metadata in theirown blades′ 252 DRAMs for fast access, but the authorities store everyupdate in their NVRAM 204 partitions on three separate blades 252 untilthe update has been written to flash 206. All the storage system writesto NVRAM 204 are in triplicate to partitions on three separate blades252 in some embodiments. With triple-mirrored NVRAM 204 and persistentstorage protected by parity and Reed-Solomon RAID checksums, the storagesystem can survive concurrent failure of two blades 252 with no loss ofdata, metadata, or access to either.

Because authorities 168 are stateless, they can migrate between blades252. Each authority 168 has a unique identifier. NVRAM 204 and flash 206partitions are associated with authorities′ 168 identifiers, not withthe blades 252 on which they are running in some embodiments. Thus, whenan authority 168 migrates, the authority 168 continues to manage thesame storage partitions from its new location. When a new blade 252 isinstalled in an embodiment of the storage cluster, the systemautomatically rebalances load by: partitioning the new blade’s 252storage for use by the system’s authorities 168, migrating selectedauthorities 168 to the new blade 252, starting endpoints 272 on the newblade 252 and including them in the switch fabric’s 146 clientconnection distribution algorithm.

From their new locations, migrated authorities 168 persist the contentsof their NVRAM 204 partitions on flash 206, process read and writerequests from other authorities 168, and fulfill the client requeststhat endpoints 272 direct to them. Similarly, if a blade 252 fails or isremoved, the system redistributes its authorities 168 among the system’sremaining blades 252. The redistributed authorities 168 continue toperform their original functions from their new locations.

FIG. 2G depicts authorities 168 and storage resources in blades 252 of astorage cluster, in accordance with some embodiments. Each authority 168is exclusively responsible for a partition of the flash 206 and NVRAM204 on each blade 252. The authority 168 manages the content andintegrity of its partitions independently of other authorities 168.Authorities 168 compress incoming data and preserve it temporarily intheir NVRAM 204 partitions, and then consolidate, RAID-protect, andpersist the data in segments of the storage in their flash 206partitions. As the authorities 168 write data to flash 206, storagemanagers 274 perform the necessary flash translation to optimize writeperformance and maximize media longevity. In the background, authorities168 “garbage collect,” or reclaim space occupied by data that clientshave made obsolete by overwriting the data. It should be appreciatedthat since authorities′ 168 partitions are disjoint, there is no needfor distributed locking to execute client and writes or to performbackground functions.

The embodiments described herein may utilize various software,communication and/or networking protocols. In addition, theconfiguration of the hardware and/or software may be adjusted toaccommodate various protocols. For example, the embodiments may utilizeActive Directory, which is a database based system that providesauthentication, directory, policy, and other services in a WINDOWS™environment. In these embodiments, LDAP (Lightweight Directory AccessProtocol) is one example application protocol for querying and modifyingitems in directory service providers such as Active Directory. In someembodiments, a network lock manager (‘NLM’) is utilized as a facilitythat works in cooperation with the Network File System (‘NFS’) toprovide a System V style of advisory file and record locking over anetwork. The Server Message Block (‘SMB’) protocol, one version of whichis also known as Common Internet File System (‘CIFS’), may be integratedwith the storage systems discussed herein. SMP operates as anapplication-layer network protocol typically used for providing sharedaccess to files, printers, and serial ports and miscellaneouscommunications between nodes on a network. SMB also provides anauthenticated inter-process communication mechanism. AMAZON™ S3 (SimpleStorage Service) is a web service offered by Amazon Web Services, andthe systems described herein may interface with Amazon S3 through webservices interfaces (REST (representational state transfer), SOAP(simple object access protocol), and BitTorrent). A RESTful API(application programming interface) breaks down a transaction to createa series of small modules. Each module addresses a particular underlyingpart of the transaction. The control or permissions provided with theseembodiments, especially for object data, may include utilization of anaccess control list (‘ACL’). The ACL is a list of permissions attachedto an object and the ACL specifies which users or system processes aregranted access to objects, as well as what operations are allowed ongiven objects. The systems may utilize Internet Protocol version 6(‘IPv6’), as well as IPv4, for the communications protocol that providesan identification and location system for computers on networks androutes traffic across the Internet. The routing of packets betweennetworked systems may include Equal-cost multi-path routing (‘ECMP’),which is a routing strategy where next-hop packet forwarding to a singledestination can occur over multiple “best paths” which tie for top placein routing metric calculations. Multi-path routing can be used inconjunction with most routing protocols, because it is a per-hopdecision limited to a single router. The software may supportMulti-tenancy, which is an architecture in which a single instance of asoftware application serves multiple customers. Each customer may bereferred to as a tenant. Tenants may be given the ability to customizesome parts of the application, but may not customize the application’scode, in some embodiments. The embodiments may maintain audit logs. Anaudit log is a document that records an event in a computing system. Inaddition to documenting what resources were accessed, audit log entriestypically include destination and source addresses, a timestamp, anduser login information for compliance with various regulations. Theembodiments may support various key management policies, such asencryption key rotation. In addition, the system may support dynamicroot passwords or some variation dynamically changing passwords.

FIG. 3A sets forth a diagram of a storage system 306 that is coupled fordata communications with a cloud services provider 302 in accordancewith some embodiments of the present disclosure. Although depicted inless detail, the storage system 306 depicted in FIG. 3A may be similarto the storage systems described above with reference to FIGS. 1A-1D andFIGS. 2A-2G. In some embodiments, the storage system 306 depicted inFIG. 3A may be embodied as a storage system that includes imbalancedactive/active controllers, as a storage system that includes balancedactive/active controllers, as a storage system that includesactive/active controllers where less than all of each controller’sresources are utilized such that each controller has reserve resourcesthat may be used to support failover, as a storage system that includesfully active/active controllers, as a storage system that includesdataset-segregated controllers, as a storage system that includesdual-layer architectures with front-end controllers and back-endintegrated storage controllers, as a storage system that includesscale-out clusters of dual-controller arrays, as well as combinations ofsuch embodiments.

In the example depicted in FIG. 3A, the storage system 306 is coupled tothe cloud services provider 302 via a data communications link 304. Thedata communications link 304 may be embodied as a dedicated datacommunications link, as a data communications pathway that is providedthrough the use of one or more data communications networks such as awide area network (‘WAN’) or local area network (‘LAN’), or as someother mechanism capable of transporting digital information between thestorage system 306 and the cloud services provider 302. Such a datacommunications link 304 may be fully wired, fully wireless, or someaggregation of wired and wireless data communications pathways. In suchan example, digital information may be exchanged between the storagesystem 306 and the cloud services provider 302 via the datacommunications link 304 using one or more data communications protocols.For example, digital information may be exchanged between the storagesystem 306 and the cloud services provider 302 via the datacommunications link 304 using the handheld device transfer protocol(‘HDTP’), hypertext transfer protocol (‘HTTP’), internet protocol(‘IP’), real-time transfer protocol (‘RTP’), transmission controlprotocol (‘TCP’), user datagram protocol (‘UDP’), wireless applicationprotocol (‘WAP’), or other protocol.

The cloud services provider 302 depicted in FIG. 3A may be embodied, forexample, as a system and computing environment that provides services tousers of the cloud services provider 302 through the sharing ofcomputing resources via the data communications link 304. The cloudservices provider 302 may provide on-demand access to a shared pool ofconfigurable computing resources such as computer networks, servers,storage, applications and services, and so on. The shared pool ofconfigurable resources may be rapidly provisioned and released to a userof the cloud services provider 302 with minimal management effort.Generally, the user of the cloud services provider 302 is unaware of theexact computing resources utilized by the cloud services provider 302 toprovide the services. Although in many cases such a cloud servicesprovider 302 may be accessible via the Internet, readers of skill in theart will recognize that any system that abstracts the use of sharedresources to provide services to a user through any data communicationslink may be considered a cloud services provider 302.

In the example depicted in FIG. 3A, the cloud services provider 302 maybe configured to provide a variety of services to the storage system 306and users of the storage system 306 through the implementation ofvarious service models. For example, the cloud services provider 302 maybe configured to provide services to the storage system 306 and users ofthe storage system 306 through the implementation of an infrastructureas a service (‘IaaS’) service model where the cloud services provider302 offers computing infrastructure such as virtual machines and otherresources as a service to subscribers. In addition, the cloud servicesprovider 302 may be configured to provide services to the storage system306 and users of the storage system 306 through the implementation of aplatform as a service (‘PaaS’) service model where the cloud servicesprovider 302 offers a development environment to application developers.Such a development environment may include, for example, an operatingsystem, programming-language execution environment, database, webserver, or other components that may be utilized by applicationdevelopers to develop and run software solutions on a cloud platform.Furthermore, the cloud services provider 302 may be configured toprovide services to the storage system 306 and users of the storagesystem 306 through the implementation of a software as a service(‘SaaS’) service model where the cloud services provider 302 offersapplication software, databases, as well as the platforms that are usedto run the applications to the storage system 306 and users of thestorage system 306, providing the storage system 306 and users of thestorage system 306 with on-demand software and eliminating the need toinstall and run the application on local computers, which may simplifymaintenance and support of the application. The cloud services provider302 may be further configured to provide services to the storage system306 and users of the storage system 306 through the implementation of anauthentication as a service (‘AaaS’) service model where the cloudservices provider 302 offers authentication services that can be used tosecure access to applications, data sources, or other resources. Thecloud services provider 302 may also be configured to provide servicesto the storage system 306 and users of the storage system 306 throughthe implementation of a storage as a service model where the cloudservices provider 302 offers access to its storage infrastructure foruse by the storage system 306 and users of the storage system 306.Readers will appreciate that the cloud services provider 302 may beconfigured to provide additional services to the storage system 306 andusers of the storage system 306 through the implementation of additionalservice models, as the service models described above are included onlyfor explanatory purposes and in no way represent a limitation of theservices that may be offered by the cloud services provider 302 or alimitation as to the service models that may be implemented by the cloudservices provider 302.

In the example depicted in FIG. 3A, the cloud services provider 302 maybe embodied, for example, as a private cloud, as a public cloud, or as acombination of a private cloud and public cloud. In an embodiment inwhich the cloud services provider 302 is embodied as a private cloud,the cloud services provider 302 may be dedicated to providing servicesto a single organization rather than providing services to multipleorganizations. In an embodiment where the cloud services provider 302 isembodied as a public cloud, the cloud services provider 302 may provideservices to multiple organizations. Public cloud and private clouddeployment models may differ and may come with various advantages anddisadvantages. For example, because a public cloud deployment involvesthe sharing of a computing infrastructure across different organization,such a deployment may not be ideal for organizations with securityconcerns, mission-critical workloads, uptime requirements demands, andso on. While a private cloud deployment can address some of theseissues, a private cloud deployment may require on-premises staff tomanage the private cloud. In still alternative embodiments, the cloudservices provider 302 may be embodied as a mix of a private and publiccloud services with a hybrid cloud deployment.

Although not explicitly depicted in FIG. 3A, readers will appreciatethat additional hardware components and additional software componentsmay be necessary to facilitate the delivery of cloud services to thestorage system 306 and users of the storage system 306. For example, thestorage system 306 may be coupled to (or even include) a cloud storagegateway. Such a cloud storage gateway may be embodied, for example, ashardware-based or software-based appliance that is located on premisewith the storage system 306. Such a cloud storage gateway may operate asa bridge between local applications that are executing on the storagearray 306 and remote, cloud-based storage that is utilized by thestorage array 306. Through the use of a cloud storage gateway,organizations may move primary iSCSI or NAS to the cloud servicesprovider 302, thereby enabling the organization to save space on theiron-premises storage systems. Such a cloud storage gateway may beconfigured to emulate a disk array, a block-based device, a file server,or other storage system that can translate the SCSI commands, fileserver commands, or other appropriate command into REST-space protocolsthat facilitate communications with the cloud services provider 302.

In order to enable the storage system 306 and users of the storagesystem 306 to make use of the services provided by the cloud servicesprovider 302, a cloud migration process may take place during whichdata, applications, or other elements from an organization’s localsystems (or even from another cloud environment) are moved to the cloudservices provider 302. In order to successfully migrate data,applications, or other elements to the cloud services provider’s 302environment, middleware such as a cloud migration tool may be utilizedto bridge gaps between the cloud services provider’s 302 environment andan organization’s environment. Such cloud migration tools may also beconfigured to address potentially high network costs and long transfertimes associated with migrating large volumes of data to the cloudservices provider 302, as well as addressing security concernsassociated with sensitive data to the cloud services provider 302 overdata communications networks. In order to further enable the storagesystem 306 and users of the storage system 306 to make use of theservices provided by the cloud services provider 302, a cloudorchestrator may also be used to arrange and coordinate automated tasksin pursuit of creating a consolidated process or workflow. Such a cloudorchestrator may perform tasks such as configuring various components,whether those components are cloud components or on-premises components,as well as managing the interconnections between such components. Thecloud orchestrator can simplify the inter-component communication andconnections to ensure that links are correctly configured andmaintained.

In the example depicted in FIG. 3A, and as described briefly above, thecloud services provider 302 may be configured to provide services to thestorage system 306 and users of the storage system 306 through the usageof a SaaS service model where the cloud services provider 302 offersapplication software, databases, as well as the platforms that are usedto run the applications to the storage system 306 and users of thestorage system 306, providing the storage system 306 and users of thestorage system 306 with on-demand software and eliminating the need toinstall and run the application on local computers, which may simplifymaintenance and support of the application. Such applications may takemany forms in accordance with various embodiments of the presentdisclosure. For example, the cloud services provider 302 may beconfigured to provide access to data analytics applications to thestorage system 306 and users of the storage system 306. Such dataanalytics applications may be configured, for example, to receivetelemetry data phoned home by the storage system 306. Such telemetrydata may describe various operating characteristics of the storagesystem 306 and may be analyzed, for example, to determine the health ofthe storage system 306, to identify workloads that are executing on thestorage system 306, to predict when the storage system 306 will run outof various resources, to recommend configuration changes, hardware orsoftware upgrades, workflow migrations, or other actions that mayimprove the operation of the storage system 306.

The cloud services provider 302 may also be configured to provide accessto virtualized computing environments to the storage system 306 andusers of the storage system 306. Such virtualized computing environmentsmay be embodied, for example, as a virtual machine or other virtualizedcomputer hardware platforms, virtual storage devices, virtualizedcomputer network resources, and so on. Examples of such virtualizedenvironments can include virtual machines that are created to emulate anactual computer, virtualized desktop environments that separate alogical desktop from a physical machine, virtualized file systems thatallow uniform access to different types of concrete file systems, andmany others.

For further explanation, FIG. 3B sets forth a diagram of a storagesystem 306 in accordance with some embodiments of the presentdisclosure. Although depicted in less detail, the storage system 306depicted in FIG. 3B may be similar to the storage systems describedabove with reference to FIGS. 1A-1D and FIGS. 2A-2G as the storagesystem may include many of the components described above.

The storage system 306 depicted in FIG. 3B may include storage resources308, which may be embodied in many forms. For example, in someembodiments the storage resources 308 can include nano-RAM or anotherform of nonvolatile random access memory that utilizes carbon nanotubesdeposited on a substrate. In some embodiments, the storage resources 308may include 3D crosspoint non-volatile memory in which bit storage isbased on a change of bulk resistance, in conjunction with a stackablecross-gridded data access array. In some embodiments, the storageresources 308 may include flash memory, including single-level cell(‘SLC’) NAND flash, multi-level cell (‘MLC’) NAND flash, triple-levelcell (‘TLC’) NAND flash, quad-level cell (‘QLC’) NAND flash, and others.In some embodiments, the storage resources 308 may include non-volatilemagnetoresistive random-access memory (‘MRAM’), including spin transfertorque (‘STT’) MRAM, in which data is stored through the use of magneticstorage elements. In some embodiments, the example storage resources 308may include non-volatile phase-change memory (‘PCM’) that may have theability to hold multiple bits in a single cell as cells can achieve anumber of distinct intermediary states. In some embodiments, the storageresources 308 may include quantum memory that allows for the storage andretrieval of photonic quantum information. In some embodiments, theexample storage resources 308 may include resistive random-access memory(‘ReRAM’) in which data is stored by changing the resistance across adielectric solid-state material. In some embodiments, the storageresources 308 may include storage class memory (‘SCM’) in whichsolid-state nonvolatile memory may be manufactured at a high densityusing some combination of sub-lithographic patterning techniques,multiple bits per cell, multiple layers of devices, and so on. Readerswill appreciate that other forms of computer memories and storagedevices may be utilized by the storage systems described above,including DRAM, SRAM, EEPROM, universal memory, and many others. Thestorage resources 308 depicted in FIG. 3A may be embodied in a varietyof form factors, including but not limited to, dual in-line memorymodules (‘DIMMs’), non-volatile dual in-line memory modules (‘NVDIMMs’),M.2, U.2, and others.

The example storage system 306 depicted in FIG. 3B may implement avariety of storage architectures. For example, storage systems inaccordance with some embodiments of the present disclosure may utilizeblock storage where data is stored in blocks, and each block essentiallyacts as an individual hard drive. Storage systems in accordance withsome embodiments of the present disclosure may utilize object storage,where data is managed as objects. Each object may include the dataitself, a variable amount of metadata, and a globally unique identifier,where object storage can be implemented at multiple levels (e.g., devicelevel, system level, interface level). Storage systems in accordancewith some embodiments of the present disclosure utilize file storage inwhich data is stored in a hierarchical structure. Such data may be savedin files and folders, and presented to both the system storing it andthe system retrieving it in the same format.

The example storage system 306 depicted in FIG. 3B may be embodied as astorage system in which additional storage resources can be addedthrough the use of a scale-up model, additional storage resources can beadded through the use of a scale-out model, or through some combinationthereof. In a scale-up model, additional storage may be added by addingadditional storage devices. In a scale-out model, however, additionalstorage nodes may be added to a cluster of storage nodes, where suchstorage nodes can include additional processing resources, additionalnetworking resources, and so on.

The storage system 306 depicted in FIG. 3B also includes communicationsresources 310 that may be useful in facilitating data communicationsbetween components within the storage system 306, as well as datacommunications between the storage system 306 and computing devices thatare outside of the storage system 306. The communications resources 310may be configured to utilize a variety of different protocols and datacommunication fabrics to facilitate data communications betweencomponents within the storage systems as well as computing devices thatare outside of the storage system. For example, the communicationsresources 310 can include fibre channel (‘FC’) technologies such as FCfabrics and FC protocols that can transport SCSI commands over FCnetworks. The communications resources 310 can also include FC overethernet (‘FCoE’) technologies through which FC frames are encapsulatedand transmitted over Ethernet networks. The communications resources 310can also include InfiniBand (‘IB’) technologies in which a switchedfabric topology is utilized to facilitate transmissions between channeladapters. The communications resources 310 can also include NVM Express(‘NVMe’) technologies and NVMe over fabrics (‘NVMeoF’) technologiesthrough which non-volatile storage media attached via a PCI express(‘PCIe’) bus may be accessed. The communications resources 310 can alsoinclude mechanisms for accessing storage resources 308 within thestorage system 306 utilizing serial attached SCSI (‘SAS’), serial ATA(‘SATA’) bus interfaces for connecting storage resources 308 within thestorage system 306 to host bus adapters within the storage system 306,internet small computer systems interface (‘iSCSI’) technologies toprovide block-level access to storage resources 308 within the storagesystem 306, and other communications resources that may be useful infacilitating data communications between components within the storagesystem 306, as well as data communications between the storage system306 and computing devices that are outside of the storage system 306.

The storage system 306 depicted in FIG. 3B also includes processingresources 312 that may be useful in executing computer programinstructions and performing other computational tasks within the storagesystem 306. The processing resources 312 may include one or moreapplication-specific integrated circuits (‘ASICs’) that are customizedfor some particular purpose as well as one or more central processingunits (‘CPUs’). The processing resources 312 may also include one ormore digital signal processors (‘DSPs’), one or more field-programmablegate arrays (‘FPGAs’), one or more systems on a chip (‘SoCs’), or otherform of processing resources 312. The storage system 306 may utilize thestorage resources 312 to perform a variety of tasks including, but notlimited to, supporting the execution of software resources 314 that willbe described in greater detail below.

The storage system 306 depicted in FIG. 3B also includes softwareresources 314 that, when executed by processing resources 312 within thestorage system 306, may perform various tasks. The software resources314 may include, for example, one or more modules of computer programinstructions that when executed by processing resources 312 within thestorage system 306 are useful in carrying out various data protectiontechniques to preserve the integrity of data that is stored within thestorage systems. Readers will appreciate that such data protectiontechniques may be carried out, for example, by system software executingon computer hardware within the storage system, by a cloud servicesprovider, or in other ways. Such data protection techniques can include,for example, data archiving techniques that cause data that is no longeractively used to be moved to a separate storage device or separatestorage system for long-term retention, data backup techniques throughwhich data stored in the storage system may be copied and stored in adistinct location to avoid data loss in the event of equipment failureor some other form of catastrophe with the storage system, datareplication techniques through which data stored in the storage systemis replicated to another storage system such that the data may beaccessible via multiple storage systems, data snapshotting techniquesthrough which the state of data within the storage system is captured atvarious points in time, data and database cloning techniques throughwhich duplicate copies of data and databases may be created, and otherdata protection techniques. Through the use of such data protectiontechniques, business continuity and disaster recovery objectives may bemet as a failure of the storage system may not result in the loss ofdata stored in the storage system.

The software resources 314 may also include software that is useful inimplementing software-defined storage (‘SDS’). In such an example, thesoftware resources 314 may include one or more modules of computerprogram instructions that, when executed, are useful in policy-basedprovisioning and management of data storage that is independent of theunderlying hardware. Such software resources 314 may be useful inimplementing storage virtualization to separate the storage hardwarefrom the software that manages the storage hardware.

The software resources 314 may also include software that is useful infacilitating and optimizing I/O operations that are directed to thestorage resources 308 in the storage system 306. For example, thesoftware resources 314 may include software modules that perform carryout various data reduction techniques such as, for example, datacompression, data deduplication, and others. The software resources 314may include software modules that intelligently group together I/Ooperations to facilitate better usage of the underlying storage resource308, software modules that perform data migration operations to migratefrom within a storage system, as well as software modules that performother functions. Such software resources 314 may be embodied as one ormore software containers or in many other ways.

Readers will appreciate that the various components depicted in FIG. 3Bmay be grouped into one or more optimized computing packages asconverged infrastructures. Such converged infrastructures may includepools of computers, storage and networking resources that can be sharedby multiple applications and managed in a collective manner usingpolicy-driven processes. Such converged infrastructures may minimizecompatibility issues between various components within the storagesystem 306 while also reducing various costs associated with theestablishment and operation of the storage system 306. Such convergedinfrastructures may be implemented with a converged infrastructurereference architecture, with standalone appliances, with a softwaredriven hyper-converged approach, or in other ways.

Readers will appreciate that the storage system 306 depicted in FIG. 3Bmay be useful for supporting various types of software applications. Forexample, the storage system 306 may be useful in supporting artificialintelligence applications, database applications, DevOps projects,electronic design automation tools, event-driven software applications,high performance computing applications, simulation applications,high-speed data capture and analysis applications, machine learningapplications, media production applications, media serving applications,picture archiving and communication systems (‘PACS’) applications,software development applications, and many other types of applicationsby providing storage resources to such applications.

For further explanation, FIG. 3C sets forth diagrams of metadatarepresentations that may be implemented as a structured collection ofmetadata objects that, together, may represent a logical volume ofstorage data, or a portion of a logical volume, in accordance with someembodiments of the present disclosure. Metadata representations 350,354, and 360 may be stored within storage array 306, and one or moremetadata representations may be generated and maintained for each ofmultiple volumes, or portions of volumes, stored within storage system306.

While other types of structured collections of the metadata objects arepossible, in this example, metadata representations may be structured asa directed acyclic graph (DAG) of nodes, where, to maintain efficientaccess to any given node, the DAG may be structured and balancedaccording to various methods. For example, a DAG for a metadatarepresentation may be defined as a type of B-tree, and balancedaccordingly in response to changes to the structure of the metadatarepresentation, where changes to the metadata representation may occurin response to changes to, or additions to, underlying data representedby the metadata representation. While in this example, there are onlytwo levels for the sake of simplicity, in other examples, metadatarepresentations may span across multiple levels and may include hundredsor thousands of nodes, where each node may include any number of linksto other nodes.

Further, in this example, the leaves of a metadata representation mayinclude pointers to the stored data for a volume, or portion of avolume, where a logical address, or a volume and offset, may be used toidentify and navigate through the metadata representation to reach oneor more leaf nodes that reference stored data corresponding to thelogical address. For example, volume 352 may be represented by metadatarepresentation 350, which includes metadata object nodes 352 and352A-352N, where leaf nodes 352A-352N include pointers to respectivedata objects, 353A-353N and 357. Data objects may be any size unit ofdata within storage array 306. For example, data objects 353A-353N and357 may each be a logical extent, where logical extents may be somespecified size, such as 1MB, 4MB, or some other size.

In this example, snapshot 356 may be created as a snapshot of volume352, where at the point in time when snapshot 356 is created, themetadata representation 354 for snapshot 356 includes all of themetadata objects for metadata representation 350 for volume 352.Further, in response to creation of snapshot 356, metadatarepresentation 354 may be designated to be read only. However, volume352 sharing the metadata representation may continue to be modified, andwhile at the moment the snapshot is created, the metadatarepresentations for volume 352 and snapshot 356 are identical, asmodifications are made to data corresponding to volume 352, and inresponse to the modifications, the metadata representations for volume352 and snapshot 356 may diverge and become different.

For example, given metadata representation 350 to represent volume 352and metadata representation 354 to represent snapshot 356, storagesystem 306 may receive an I/O operation that writes to data that isultimately stored within data object 353B, where data object 353B ispointed to by leaf node pointer 352B, and where leaf node pointer 352Bis part of both metadata representations 350 and 354. In response to thewrite operation, the read only data objects referred to by metadatarepresentation 354 remain unchanged, and pointer 352B may also remainunchanged. However, metadata representation 350 is modified to include anew data object to hold the data written by the write operation, wherethe modified metadata representation is depicted as metadatarepresentation 360. Further, the write operation may be directed to onlya portion of data object 353B, and consequently, the new data object 357may include a copy of data object 353B in addition to the payload forthe write operation.

In this example, as part of processing the write operation, metadatarepresentation 360 for volume 352 is modified to remove metadata objectpointer 352B and to include new metadata object pointer 358, wheremetadata object pointer 358 is configured to point to data object 357,where data object 357 stores the data written by the write operation.Further, metadata representation 360 continues to include all metadataobjects included within metadata representation 350-with the exclusionof metadata object pointer 352B, where metadata object 352B continues toreference read only data object 353B.

In this way, using metadata representations, a volume or a portion of avolume may be considered to be snapshotted, or considered to be copied,by creating metadata objects, and without actual duplication of dataobjects-where the duplication of data objects may be deferred until awrite operation is directed at one of the read only data objectsreferred to by the metadata representations.

In other words, an advantage of using a metadata representation torepresent a volume is that a snapshot or a copy of a volume may becreated and be accessible in constant order time, and specifically, inthe time it takes to create a metadata object for the snapshot or copy,and to create a reference for the snapshot or copy metadata object tothe existing metadata representation for the volume being snapshotted orcopied. As described further below, a virtualized copy-by-referencemakes use of a metadata representation in a manner that is similar tothe use of a metadata representation in creating a snapshot of avolume-where a metadata representation for a virtualizedcopy-by-reference may often correspond to a portion of a metadatarepresentation for an entire volume.

An example implementation of virtualized copy-by-reference may be withinthe context of a virtualized storage system, where multiple block rangeswithin and between volumes may reference a unified copy of stored data.In such an environment, it is advantageous to leverage that capabilityas part of implementing SCSI offloaded data copy operations.

For example, SCSI SPC-4/SPC-3 specifications describe two basicmechanisms to support storage systems copying data within and betweenstorage devices without the data being copied through a host-such as bythe host issuing read and write requests from a source device to atarget device.

The first mechanism may be with a set of described EXTENDED COPYcommands that may be sent to a copy manager that names a source deviceand a source block range and a target device and a target block range,where the extended copy command directs the copy manager to copy blocksfrom the source to target directly rather than further involving thehost that issued the EXTENDED COPY command. In this example, a copymanager may be integrated within a source device or a target device,where the copy manager may be a hardware or software component.

A second mechanism uses a more complex set of commands, where a hostobtains and supplies tokens in order to describe a secured source ofdata and supply that secured that secured description to a copy targetor copy manager. This second mechanism may further provide someassurances of source data stability during a copy operation-therebyreducing or eliminating modifications due to, for example, concurrentWRITE activity.

To continue this example, a ROD token, as used below, is a“Representation of Data” token, which may be a data structure thatrepresents a block range associated with a source or target of a datatransfer. A ROD may specify a copy manager, a logical unit associatedwith a collection of blocks, a type, and copy manager-specific data thatthe copy manager may use to understand and handle transfers associatedwith a source or target dataset. A ROD token may includecryptographically secure signatures to ensure their content cannot beforged.

An application or server may copy a range of clocks from a source blockrange of a source device to a target block range of the same sourcedevice or to a different device using the following steps:

1. A host issues a POPULATE TOKEN command from a SCSI initiator port toa SCSI target port supplying a first 32-bit LIST IDENTIFIER, anINACTIVITY TIMEOUT, a ROD type, and a list of block range descriptorsthat may each include a logical block address and a number of logicalblocks. The ROD type may indicate some level of required stability for asource dataset, which may specify how overwrites of block ranges may behandled.

2. A host issues a RECEIVE ROD TOKEN INFORMATION command from the sameSCSI initiator port to the same SCSI target port as in the step 1, andmay include a same LIST IDENTIFIER to retrieve a set of secured, timelimited ROD token descriptors that represent a source storage device’sview into each block range covered by the POPULATE TOKEN command in step1.

3. Some host, which may be the same host as in the previous steps or adifferent host, may issue a SCSI WRITE USING TOKEN command that suppliesa second LIST IDENTIFIER, and that may include a copy of a secured tokenas received in step 2, and supplying a list of block range descriptorsthat describe a range of blocks to write data into from the blocksreferenced in step 1 that correspond to the token.

4. The host from step 3 may issue some number of RECEIVE COPY STATUScommands through the same SCSI initiator and target ports and giving thesame LIST IDENTIFIER as in step 3 to monitor progress of the copyoperation, such as to display a percentage completion and an estimatefor when the copy operation may complete. A RECEIVE ROD TOKENINFORMATION request may be used in addition, or instead, to get morestatus detail and progress about the copy.

The source, as described in steps 1 and 2, and the target, as describedin step 3, may be in the same storage system-for example, between twoblock ranges of a same volume or between volumes on a same storagearray. Alternately, the source and target may be between volumes on twodifferent storage arrays. The SCSI specification also allows use of acopy manager for steps 1 through 4 that is separate from the SCSIstorage system associated with the data. The SCSI specification alsoallows for a separate copy manager running on distinct SCSI devices forsteps 1 and 2 or for steps 3 and 4; however, the standard does notsuggest exactly how separate copy managers and devices transfer databetween them, or how exactly they would validate tokens between eachother if all these steps aren’t in the same SCSI target storage systems.

The POPULATE TOKEN command may include various parameters, including:

-   A list of block range descriptors to establish a collection of    blocks associated with a SCSI volume that are logically concatenated    to form a logical set of blocks, which are defined in terms of some    fundamental block size associated with the device. For example,    given a volume with a 512 byte block size, a block range with an LBA    of 2000 with a block count of 100 coupled with a second block range    of LBA 8000 count 200 may represent 300 logical blocks (a total of    153 600 bytes) segmented between 102,400 bytes at byte offset    1,024,000 and 204,800 bytes at byte offset 4,096,000.-   An INACTIVITY TIMEOUT may be a maximum lifespan through which a    token will remain valid after the last request to the storage device    that uses the token. The token can become invalid earlier, and for    any reason. The purpose of the inactivity timeout may be as a    security measure to prevent a leaked token from being useful in the    future.-   A ROD type may specify the degree to which the application expects    the storage target to keep the stored content backed by the token    durable (surviving long enough to complete the copy operation) or    stable (remaining unchanged throughout the operation). Further:    -   o A ROD type of access upon reference indicates that the storage        device should not be concerned with changes to blocks from the        time of the POPULATE TOKEN request to the time blocks are        copied.    -   o A ROD type of point in time copy-change vulnerable indicates        that the storage device should invalidate a token if a change        such as a write request modifies the source content associated        with a token and if the storage device cannot inexpensively        preserve the original content-in other words, any copy must be        from unmodified blocks, but the application accepts that any        modification may cause the copy to fail.    -   o A ROD type of point in time copy persistent indicates that the        storage device should preserve the source content associated        with a token, such as by taking an actual point-in-time snapshot        of the data. The time associated with the preserved content is        somewhere between the time when the storage device receives the        POPULATE TOKEN command and the time the storage device responds        to the RECEIVE ROD TOKEN INFORMATION command in step 2 above.        Even with a persistent point-in-time copy token, the storage        device may invalidate a token for any number of reasons,        including because it was mildly expensive to maintain it or a        controller rebooted-so, the specification doesn’t really demand        that it be all that persistent.

A ROD token may be retrieved through the RECEIVE ROD TOKEN INFORMATIONcommand rather than being in response data to the POPULATE TOKENcommand. The RECEIVE ROD TOKEN INFORMATION command retrieves a set ofROD tokens that cover the block range descriptors from the originalPOPULATE TOKEN request, matched up by initiator/target port and LISTIDENTIFIER. It also retrieves status information, including completionstatus, how much data has been copied, and additional information thatcan be used to get an estimated time on when any copying might complete.

AWRITE USING TOKEN command supplies one of the ROD tokens from thetokens associated with the POPULATE TOKEN request and uses that assource data as the dataset to copy into a set of target blocks, under anew LIST IDENTIFIER. The description of the target dataset is similarenough to how the source dataset is described to POPULATE TOKEN that thesame ROD token mechanism can be used to retrieve status information.

Different embodiments of virtualized copy-by-reference may beimplemented within different storage systems. An example storage systemmay reference stored data in one or both of two ways: one, as a set ofidentified logical extents which can be attached to virtual addressspaces of a volume and which can be logically referenced within andbetween volumes in the storage system; and/or two, as a set ofreferences to physically stored data blocks that may or may not becompressed, are not overwritten in place without first being recoveredfor reuse, and that may or may not be combined in various ways withother stored data blocks, and where multiple ranges of one or morevolumes (or of one or more logical extents) can reference those storeddata blocks thus resulting in those physical blocks being shared betweenmultiple volume ranges, multiple volumes or multiple logical extents.When these two mechanisms (logical extents and references to physicallystored data blocks) are combined, then logical extents comprisereferences to stored data blocks, and overwrites may store newreferences to stored data blocks. Further, logical extents can be markedas “copy on write” which may create a new logical extent when thelogical extent in the context of a volume or of larger composite logicalextent is written or otherwise modified, by copying data blockreferences for unchanged content and forming new block references formodified content.

Logical extents may be combined in various ways, including as simplecollections or as logically related address ranges within somelarger-scale logical extent that is formed as a set of logical extentreferences. These larger combinations could also be given logical extentidentities of various kinds, and could be further combined into stilllarger logical extents or collections. A copy-on-write status couldapply to various layers, and in various ways depending on theimplementation. For example, a copy on write status applied to a logicalcollection of logical collections of extents might result in a copiedcollection retaining references to unchanged logical extents and thecreation of copied-on-write logical extents (through copying referencesto any unchanged stored data blocks as needed) when only part of thecopy-on-write logical collection is changed.

Deduplication, volume snapshots, or block range snapshots may beimplemented in this model through combinations of referencing storeddata blocks, or referencing logical extents, or marking logical extents(or identified collections of logical extents) as copy-on-write.

Some garbage collection models may be implemented to reclaim data blocksthat are no longer in use, such as due to all copies having been deletedor overwritten or such as due to the last reference to an identifiedlogical extent having been deleted or replaced. Garbage collection mayoperate in a variety of ways, including mark-and-sweep, referencecounting, or through any number of other techniques.

Further, with flash storage systems, stored data blocks may be organizedand grouped together in various ways as collections are written out intopages that are part of larger erase blocks. Eventual garbage collectionof deleted or replaced stored data blocks may involve moving contentstored in some number of pages elsewhere so that an entire erase blockcan be erased and prepared for reuse. This process of selecting physicalflash pages, eventually migrating and garbage collecting them, and thenerasing flash erase blocks for reuse may or may not be coordinated,driven by, or performed by the aspect of a storage system that is alsohandling logical extents, deduplication, compression, snapshots, virtualcopying, or other storage system functions. A coordinated or drivenprocess for selecting pages, migrating pages, garbage collecting anderasing erase blocks may further take into account variouscharacteristics of the flash memory device cells, pages, and eraseblocks such as number of uses, aging predictions, adjustments to voltagelevels or numbers of retries needed in the past to recover stored data.They may also take into account analysis and predictions across allflash memory devices within the storage system.

In other examples, such as with persistent point-in-time copy tokensbased on copied references, a SCSI EXTENDED COPY request may beimplemented by making purely virtual copies by reference from one volumeblock range to another block range within the same volume or to adifferent volume (or, with synchronous replication between ranges ofvolumes that are replicated between two or more storage devices). Thesereferences copy stored data block references, logical extent references,or combinations of the two, and may mark logical extents ascopy-on-write as necessary to ensure that future writes will result indistinct logical extents. This type of implementation may be extended tosupport persistent point-in-time copy ROD types.

For example, to do so, a variant of the mechanism described for EXTENDEDCOPY may virtually copy the set of volume block address ranges listed inthe POPULATE TOKEN request to some out-of-band space that is outside ofany volumes that are exported by hosts. For example, these could be tospecial volumes that are not exported, or these could simply be tocollections of logical extents that are not associated with any volumes,including simply a collection of logical extents associated entirelywith the POPULATE TOKEN request. Alternately, these could simply belists of references to physically stored data blocks organized invarious ways.

In this example, these virtual copies may then be given a lifespan thatis extended with each relevant SCSI interaction by the amount of theINACTIVITY TIMEOUT value, or they may be kept around for some fixedmaximum lifespan. After the lifespan of the virtual copy has expired,the address range can be unmapped or deleted. If a collection of logicalextents is assigned specifically for the copy request, then thatcollection could simply be removed. After the address range is unmappedor the logical extent collection is removed, those virtually copiedblocks will no longer reference the associated data. Until then, thevirtual copy will hold that reference and will prevent overwritten orsubsequently unmapped blocks in the source ranges from being garbagecollected.

In some examples, it may be beneficial to copy all source blocksassociated with a POPULATE TOKEN request (e.g., all blocks in all theblock range descriptors) into a single sequential target address rangein the out-of-band volume or logical extent collection.

Further, a RECEIVE ROD TOKEN INFORMATION may then retrieve an encodingof the addressing information associated with this virtual copy,possibly as a volume offset for the special volumes that aren’t exportedto hosts, or possibly as an identified logical extent or logical extentcollection and an extent or collection offset if no volume is used, orpossibly as a logical extent collection identifier that is solely of usefor this copy.

Given that the point-in-time of the blocks mapped by a token may beanywhere between the time a storage device receives a POPULATE TOKENcommand and the time it sends the response to the RECEIVE ROD TOKENINFORMATION command, the virtual copy may take place during theprocessing of the POPULATE TOKEN command, during the processing of theRECEIVE ROD TOKEN INFORMATION command, or anywhere in between. Thecombination of a SCSI I_T Nexus and a 32-bit LIST IDENTIFIER identifiesthe request. As an example, the LIST IDENTIFIER may be held in memory onthe array controller along with the list of block ranges and the token’stimespan until the RECEIVE ROD TOKEN INFORMATION command is received, ora virtual copy could be persistently associated with the LIST IDENTIFIERand the token lifespan. For example, if a logical extent collection isassociated with the token, then the logical extent collection could bepersisted in association with the LIST IDENTIFIER and a token lifespanduring processing of the POPULATE TOKEN command.

Further, a WRITE USING TOKEN command sent to the same array as thePOPULATE TOKEN command, even if to different volumes or from a differenthost port or a different array target port (or, with a synchronouslyreplicated array even to a port on a different array) may then virtuallycopy from the out-of-band space represented by the source token to thetarget volumes using the same or a similar mechanism. In the case of alogical extent collection and/or stored data block referenceimplementation, this could either replace any existing medium extentsassociated with the target volume addresses (if there are any) withreferences to the virtually copied medium extents resulting from theearlier POPULATE TOKEN command, or this could replace any stored datablock references covering the target region of the copy (if there areany) with the copied stored data block references. If the token isintended for only one use, then the logical extent references could becopied into the target volume with or without marking either theout-of-band medium reference or the new reference as copy-on-write. Theoriginal logical extent reference that is the data source for thePOPULATE TOKEN command can remain copy-on-write, ensuring that anoverwrite to the original volume will preserve the stability of the dataunderlying the copied reference.

In another example, a WRITE USING TOKEN command sent to some other arraymay use the token information to rendezvous back to the source array andcould use the token as a data source for an array-to-array copyoperation.

In general, virtualized copy-by-reference uses a method for virtuallycopying a range of blocks to some address range outside of any exportedvolumes, such that any overwrites of the source range will not disturbthe virtually copied block range, and such that when the virtuallycopied block range is released on some way, any held blocks that are nolonger used by the source range (or elsewhere in the storage system) maybe garbage collected in some way. This implementation is specificallydistinct from whole volume snapshot or clone based copy-on-write imagesbecause the number of blocks affected by copy-on-write overwritepolicies is restricted to the small number of blocks covered by theblock range descriptors. It is also distinct in that it is based on arelated or underlying technique for doing virtual block range copies forSCSI EXTENDED COPY requests that would not itself be suitable for wholevolume snapshots.

In different implementation, various mechanisms may be used to delayinternal operations associated with these virtual copies. If the copieshappen quickly enough, then intermediate data structures could belargely elided. For example, a record of a virtual copy could bepersisted to a fast commit area (e.g., some representation of theoriginating virtual copy request associated with the POPULATE TOKENcommand and/or some representation of the copy request into the targetvolume address ranges could be written to a fast non-volatile journalingdevice), and the source address range could be monitored for overwrites.If the source address isn’t overwritten, then the intermediate mediums(or other more complex, persistent metadata tracking structures) may notbe needed, and multi-phase token-based copies could be effectivelyshort-circuited into a direct source-to-target address range virtualcopy. More complex intermediate copy-on-write type structures might bewritten in the case of a write (or TRIM/UNMAP, or copy) to an addressrange within block address ranges of the source blocks, or if the tokenlifespan extends long enough in time that it becomes expensive tomaintain an in-memory representation (or a held journal entry) for theintermediate virtual copy. As a result, much of what is describedpreviously in the logical extent and stored data block reference copiesbased on the use of intermediate volumes or logical extent collectionsor stored data block collections might be represented in memory, butmight often be persisted only as one or a few journal entries written toensure that operations are fault recoverable. However, they might bemore completely represented in persistent storage if the copy takeslonger and associated data structures are flushed to backing store tomake room in memory or on journaling devices for other operations.

For further explanation, FIG. 4 sets forth a flow chart illustrating anexample method for virtualized copy-by-references according to someembodiments of the present disclosure. Although depicted in less detail,storage system 306 depicted in FIG. 4 may be similar to the storagesystems described above with reference to FIGS. 1A-1D, FIGS. 2A-2G,FIGS. 3A-3C, or any combination thereof. Further, the storage systemdepicted in FIG. 4 may include the same, fewer, additional components asthe storage systems described above.

By contrast, a virtualized copy-by-reference greatly improves, in somecases, by orders of magnitude, the speed at which source data from asource volume may be available at a target volume following completionof a virtualized copy-by-reference of the source data from the sourcevolume to the target volume. In some examples, to carry out the fasteravailability of the source data at the target volume, instead oftransferring the source data from a source volume to a target volume, ametadata representation of the source data is transferred to the targetvolume. Generally, metadata representations of source data may be muchsmaller in size than the actual source data, where using the metadatarepresentation of the source data stored in the target volume allows thetarget volume to service requests for the source data. In this example,a metadata representation is similar to the metadata representationsdescribed above with reference to FIG. 3C. Because the target volumeuses the metadata representation of the source data to access the sourcedata, copying one or more portions of the source data from the sourcevolume to the target volume may be deferred. In some cases, the transferof one or more portions of the source data from a source volume to atarget volume may be deferred until some portion of the source data ismodified at the source volume. Generally, a size for source data may bearbitrary.

The example method depicted in FIG. 4 includes receiving (404), from afirst computer system 452, a request 454 for reference information forsource data 456 stored within a source volume 458. Receiving (404)request 454 may be implemented using one or more communication protocolsfor transporting packets or data across a network, such as storage areanetwork 158, or such as the Internet, or any suitable network acrosswhich a computing device may communicate with storage system 306. Inthis example, request 454 may be a command sent from a SCSI port oncomputer system 306 to a SCSI port on storage system 306. Further, inthis example, the request 454 may indicate various parameters, includingan indication of a block range, or more generally, a memory addressrange, an indication of a timeout value, an indication of a commandtype, and an identifier that corresponds with the request, among otherparameters. In this example, a memory address range may specify anoffset into a volume and a number of bytes or blocks, or the memoryaddress range may specify a start address and a number of bytes orblocks. In this example, a timeout parameter may indicate a period oftime in which any information provided to first computer system 452 isvalid, whereupon expiration of the timeout, any attempted use of theprovided information may result in an error or indication of invalidity.In this example, a command type may indicate a degree to which thesource data is expected to remain durable. For example, a command typemay indicate that the source volume need not prevent changes to sourcedata upon receipt of the request 454 indicating a request for referenceinformation for the source data; a command type may also indicate thatany reference information provided in response be invalidated if thesource data is modified before the reference information is used beforea timeout; a command type may also indicate that the source data shouldbe preserved until the reference information is used or until a timeoutexpires. In this example, an identifier may be used by first computersystem 452, storage system 306, and computer system 464 to refer to asame transaction initiated by the request, and a same set of sourcedata.

The example method depicted in FIG. 4 also includes providing (406), tofirst computer system 452, reference information 460 for metadatarepresentation 462 of source data 456. Providing (406) referenceinformation 460 for metadata representation 462 of source data 456 maybe implemented using different techniques. For example, in onetechnique, storage system 306 may provide sufficient information withinreference information 460 such that storage system 306, without storingreference information 460, may subsequently process and handle a commandor request to copy or move source data 456 from source volume 458 intotarget volume 468 using reference information 460. In this example,reference information 460 may be generated to include a keyed-hashmessage authentication code (HMAC), where subsequent commands thatinclude the keyed-hash message authentication code may be authenticatedby validating the keyed-hash authentication code in the command. In thisway, the responsibility for keeping track of the authenticationinformation is offloaded from storage system 306. In other examples,different types of encrypted authentication protocols may be used toauthenticate requests.

In another example, providing (406) reference information 460 may beimplemented by storage system 306 using an identifier corresponding torequest 454, and corresponding the identifier with metadatarepresentation 462, where metadata representation 462 corresponds tosource data 456. For example, storage system 306 may create and maintaina list of transactions storing records that may be indexed using anidentifier, where stored records may include information received in arequest 454, and where individual records may include a reference tometadata representations within source volume 458. In this way, storagesystem 306 maintains information for mapping an identifier toinformation usable to complete a request to move or copy data from asource volume to a target volume.

Further, to carry out generating metadata representation 462, storagesystem 306 may identify a portion of a metadata representation forsource volume 458 storing source data 456, where the portion may, insome cases, be the entire source volume 458. Further the portion of themetadata representation for source volume 458 may be identified by usingmemory address data for source data 456 to traverse the structuredcollection of metadata objects to find the nodes that correspond to thedata objects for the memory address data for source data 456. Further, ametadata object root node for metadata representation 462 may be createdthat refers to one or more nodes within the metadata representation forentire source volume 458, where the metadata object root node mayspecify portions of one or more nodes within the metadata representationfor entire source volume 458, or may specify other indications forreferencing only the portions of the metadata representation for entiresource volume 458 that correspond to source data 456. In this way,reference information 460 may include an identifier that corresponds tometadata representation 462, where reference information 460, includingthe identifier, may later be used by another computer system to continuethe virtualized copy-by-reference.

The example method depicted in FIG. 4 also includes receiving (408),from second computer system 464, request 466 that indicates a request towrite source data 456 to target volume 468, where request 466 indicatesreference information 460. Receiving (408) request 466 may beimplemented by using one or more communication protocols fortransporting packets or data across a network, such as storage areanetwork 158, or such as the Internet, or any suitable network acrosswhich a computing device may communicate with storage system 306. Inthis example, request 466 may be a command sent from a SCSI port oncomputer system 464 to a SCSI port on storage system 306.

Further, reference information 460, provided by second computer system464, may have been received at second computer system 464 from firstcomputer system 452, as depicted by reference information 460 movingfrom first computer system 452 to second computer system 464, wheresecond computer system 464 provides reference information 460 to storagesystem 306 within request 466.

Further still, in this example, receiving (408) may not follow directlyfrom providing (406) reference information 460 for metadatarepresentation 462 to first computer system 452 because the threecomputer systems, storage system 306, first computer system 452, andsecond computer system 464 may process and perform various otheroperations in between the depicted steps. However, depicted steps(404)-(410) are ultimately performed in carrying out a virtualizedcopy-by-reference.

While in this example, the operation depicted in step (408) is a writeoperation, other operations may be substituted with equal effect, forexample, instead of a write operation, request 466 may indicate a writecommand, a move command, a transfer command, or some other commandindicative of continuation of the virtualized copy-by-referencecorresponding to reference information 460.

The example method depicted in FIG. 4 also includes copying (410), usingreference information 460, metadata representation 462 of source data456 to target volume 468. Copying (410) metadata representation 462 ofsource data 456 to target volume 468 may be implemented by indexing arecord within a stored list of transactions using the identifierincluded within reference information 460 that was earlier provided(406) with regard to a same virtualized copy-by-reference. In otherwords, the identifier within reference information 460 may serve as anindex into a list of transactions corresponding to multiple requests forreference information for multiple, respective virtualizedcopy-by-references, and where a record within the list of transactionsmay include some or all of the information provided in request 454, inaddition to other information generated by storage system 306. In otherexamples, the identifier may be correlated to a virtualizedcopy-by-reference in other ways.

Copying (410) metadata representation 462 of source data 456 to targetvolume 468 may be further implemented by using the record stored at theindexed list of transactions to access stored reference information foraccessing metadata representation 462, and copying the metadata objectscorresponding to metadata representation 462 into target volume 468. Inthis example, metadata representation 462 may be stored within sourcevolume 458, however, in other examples, and as discussed below, metadatarepresentation 462 may be copied from source volume 458 to anintermediary volume in response to receiving (404) the request, whereaccordingly, copying (410) metadata representation 462 would includecopying metadata representation 462 from the intermediary volume totarget volume 468.

In this way, at this point within the virtualized copy-by-reference,second computer system 464 may have access to source data 456 withoutany data objects corresponding to source data 456 stored within sourcevolume 458 being copied from source volume 458 to target volume 468.

For further explanation, FIG. 5 sets forth a flow chart illustrating anexample method of virtualized copy-by-references according to someembodiments of the present disclosure. The example method depicted inFIG. 5 is similar to the example method depicted in FIG. 4 , as theexample method depicted in FIG. 5 also includes: receiving (404), from afirst computer system 452, a request 454 for reference information forsource data 456 stored within a source volume 458; providing (406), tofirst computer system 452, reference information 460 for metadatarepresentation 462 of source data 456; receiving (408), from secondcomputer system 464, request 466 that indicates a request to writesource data 456 to target volume 468, where request 466 indicatesreference information 460; and copying (410), using referenceinformation 460, metadata representation 462 of source data 456 totarget volume 468.

However, the example method depicted in FIG. 5 further includes,responsive to request 454 for reference information for source data 456,copying (502) metadata representation 462 of source data 456 from sourcevolume 458 to intermediary volume 552, and specifying that copying (410)metadata representation 462 to target volume 468 includes copying (504)metadata representation 462 from intermediary volume 552 to targetvolume 468.

Copying (502) metadata representation 462 of source data 456 from sourcevolume 458 to intermediary volume 552 may be implemented similarly tocopying (410) metadata representation 462 of source data 456 to targetvolume 468 described above with reference to FIG. 4 -where instead ofcopying (410) metadata representation 462 into target volume 468,metadata 462 is copied into intermediary volume 552.

Further intermediary volume 552 may be invisible, or inaccessible, tousers of storage system 306, and intermediary volume 552 may be one ofmultiple intermediary volumes. In the case where there are multipleintermediary volumes, reference information 460 may further include anintermediary volume identifier and offset for locating metadatarepresentation 462 stored within one of the intermediary volumes.Further, given multiple intermediary volumes, the intermediary volumesmay be lockless, where access to stored metadata representations may beprovided by cycling storage of metadata representations through themultiple intermediary volumes. For example, in a case where there arefour intermediary volumes, a given metadata representation may be storedat a current offset within a current volume at a current time, wheresubsequent to storage of the given metadata representation, the currentoffset may be incremented by a size of the given metadatarepresentation. Further in this example, additional metadatarepresentations may be written to the current volume until a window oftime from the current time has elapsed, at which point, the currentvolume may be specified to be a next intermediary volume within arotation of the multiple intermediary volumes, and the current offsetmay be specified to a beginning of the current intermediary volume. Aquantity and size of the multiple intermediary volumes may be specifiedto hold an expected number of metadata representations for an expectednumber of virtualized copy-by-reference over a period of time thatincludes a period of time for validity of reference information thatincludes references to an intermediary volume and offset of a metadatarepresentation within an intermediary volume. While this example isbased on using four intermediary volumes, in other examples, more orfewer intermediary volumes may be specified in dependence upon anexpected quantity of space needed to service an expected number ofvirtualized copy-by-references over a given period of time.

Further, in this example, instead of a record within a list oftransactions storing a reference to metadata representation 462 withinsource volume 458, as described with reference to FIG. 4 , a recordcreated within the list of transactions may store reference informationto metadata representation 462 stored within intermediary volume 552,where the identifier is used to index into the list of transactions.

Given that metadata representation 462 is stored within intermediaryvolume 552, copying (410) metadata representation 462 to target volume468 includes copying (504) metadata representation 462 to target volume468. Copying (504) metadata representation 462 includes using thereference location in the indexed record to identify the storagelocation of metadata representation 462 within intermediary volume 552,and using that reference location as a source for a copy of metadatarepresentation 462 into target volume 468.

For further explanation, FIG. 6 sets forth a flow chart illustrating anexample method of a virtualized copy-by-reference according to someembodiments of the present disclosure. The example method depicted inFIG. 6 is similar to the example method depicted in FIG. 4 , as theexample method depicted in FIG. 6 also includes: receiving (404), from afirst computer system 452, a request 454 for reference information forsource data 456 stored within a source volume 458; providing (406), tofirst computer system 452, reference information 460 for metadatarepresentation 462 of source data 456; receiving (408), from secondcomputer system 464, request 466 that indicates a request to writesource data 456 to target volume 468, where request 466 indicatesreference information 460; and copying (410), using referenceinformation 460, metadata representation 462 of source data 456 totarget volume 468.

However, the example method depicted in FIG. 6 further includes,responsive to write request 652 directed at a particular data object654A of a plurality of data objects 654A-654N, copying (602) at least aportion of the particular data object 654A from a source location insource volume 456 to a target location in target volume 468. In somecases, the source location and the target location may be differentmemory addresses, or different offsets within a volume.

Copying (602) at least the portion of particular data object 654A fromthe source location in source volume 458 to the target location intarget volume 468 may be implemented by using addressing informationwithin write request 652 to navigate metadata representation 462 toreach a leaf node corresponding to particular data object 654A. While inthis example, a single data object corresponds to the memory addressinginformation in write request 652, in other examples, a write operationmay be directed at data stored within multiple data objects of ametadata representation.

Further, given identification of particular data object 654A, new dataobject 656 may be created on target volume 468, and the data may becopied from source volume 468 into new data object 656 stored withintarget volume 468.

Responsive to creating data object 656, where data object 656 storesdata that is to be overwritten by write request 652, metadatarepresentation 462, stored within target volume 468, may be updated toreflect that the leaf node within metadata representation 462 thatpreviously referred to data object 654A should be updated, or modified,to refer to new data object 656, stored within target volume 468.Updating metadata representation 462 is further described with referenceto FIG. 7 .

For further explanation, FIG. 7 sets forth a flow chart illustrating anexample method of a virtualized copy-by-reference according to someembodiments of the present disclosure. The example method depicted inFIG. 7 is similar to the example method depicted in FIG. 6 , as theexample method depicted in FIG. 7 also includes: receiving (404), from afirst computer system 452, a request 454 for reference information forsource data 456 stored within a source volume 458; providing (406), tofirst computer system 452, reference information 460 for metadatarepresentation 462 of source data 456; receiving (408), from secondcomputer system 464, request 466 that indicates a request to writesource data 456 to target volume 468, where request 466 indicatesreference information 460; copying (410), using reference information460, metadata representation 462 of source data 456 to target volume468; and responsive to write request 652 directed at a particular dataobject 654A of a plurality of data objects 654A-654N, copying (602) atleast a portion of the particular data object 654A from a sourcelocation in source volume 456 to a target location in target volume 468.

However, the example method depicted in FIG. 7 further includes,responsive to copying (602) the particular data object 654A from asource location in source volume 458 to a target location in targetvolume 468, updating (702) metadata representation 652 of the sourcedata stored in the target volume to indicate that the particular dataobject 654A is stored in target volume 468 instead of source volume 458.

Updating (702) metadata representation 462 may be implemented by usingaddressing information within write request 652 to navigate metadatarepresentation 462 to reach a leaf node corresponding to particular dataobject 654A, and replacing reference information within the leaf node toreference data object 656 instead of data object 654A—where data object656 was created to store information copied from data object 654A onsource volume 458. In this example, updated metadata representation 652is depicted in FIG. 7 as metadata representation 752. While in thisexample, a single data object corresponds to the memory addressinginformation in write request 652, in other examples, a write operationmay be directed at data stored within multiple data objects of ametadata representation.

For further explanation, FIG. 8 sets forth a flow chart illustrating anexample method of a virtualized copy-by-reference according to someembodiments of the present disclosure. The example method depicted inFIG. 8 is similar to the example method depicted in FIG. 4 , as theexample method depicted in FIG. 8 also includes: receiving (404), from afirst computer system 452, a request 454 for reference information forsource data 456 stored within a source volume 458; providing (406), tofirst computer system 452, reference information 460 for metadatarepresentation 462 of source data 456; and receiving (408), from secondcomputer system 464, request 466 that indicates a request to writesource data 456 to target volume 468, where request 466 indicatesreference information 460.

However, the example method depicted in FIG. 8 does not include copying(410) metadata representation 462, and further includes, generating(802), using reference information 460, reference 852 within targetvolume 468 to metadata representation 462 of the source data withinsource volume 458.

Generating (802) reference 852 within target volume 468 to metadatarepresentation 462 of the source data within source volume 458 may beimplemented by creating a metadata object that corresponds with a memoryaddress range corresponding with a memory address range of source data456, where the metadata object is configured to reference metadatarepresentation 462. For example, in a manner similar to how a metadataobject 358 in FIG. 3C may reference an existing metadata representation350 for volume 352, the created metadata object may include reference852 to reference metadata representation 462.

In this way, data corresponding to source data 456 may be accessed fromtarget volume 468 without copying over a metadata representation forsource data 456 that is stored within source volume 458. Further, anadvantage is that the overhead for providing this access is a constantorder number of instructions for creating the metadata object andreference 852.

Example embodiments are described largely in the context of a fullyfunctional computer system for migrating applications executing on astorage system. Readers of skill in the art will recognize, however,that the present disclosure also may be embodied in a computer programproduct disposed upon computer readable storage media for use with anysuitable data processing system. Such computer readable storage mediamay be any storage medium for machine-readable information, includingmagnetic media, optical media, or other suitable media. Examples of suchmedia include magnetic disks in hard drives or diskettes, compact disksfor optical drives, magnetic tape, and others as will occur to those ofskill in the art. Persons skilled in the art will immediately recognizethat any computer system having suitable programming means will becapable of executing the steps of the method as embodied in a computerprogram product. Persons skilled in the art will recognize also that,although some of the example embodiments described in this specificationare oriented to software installed and executing on computer hardware,nevertheless, alternative embodiments implemented as firmware or ashardware are well within the scope of the present disclosure.

Embodiments can include a system, a method, and/or a computer programproduct. The computer program product may include a computer readablestorage medium (or media) having computer readable program instructionsthereon for causing a processor to carry out aspects of the presentdisclosure.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present disclosure may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user’scomputer, partly on the user’s computer, as a stand-alone softwarepackage, partly on the user’s computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user’s computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present disclosure.

Aspects of the present disclosure are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to some embodimentsof the disclosure. It will be understood that each block of theflowchart illustrations and/or block diagrams, and combinations ofblocks in the flowchart illustrations and/or block diagrams, can beimplemented by computer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present disclosure. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

Readers will appreciate that the steps described herein may be carriedout in a variety of ways and that no particular ordering is required. Itwill be further understood from the foregoing description thatmodifications and changes may be made in various embodiments of thepresent disclosure without departing from its true spirit. Thedescriptions in this specification are for purposes of illustration onlyand are not to be construed in a limiting sense. The scope of thepresent disclosure is limited only by the language of the followingclaims.

What is claimed is:
 1. A method comprising: receiving a request to writethe source data to a target volume, wherein the request to write thesource data indicates the reference information; obtaining a metadatarepresentation of the source data using the reference information; andcopying, using the reference information, the metadata representation ofthe source data to the target volume.
 2. The method of claim 1, whereinthe metadata representation of the source data is a structuredcollection of metadata objects referring, respectively, to data objectscomprising the source data, and wherein the data objects are storedwithin the source volume.
 3. The method of claim 1, wherein thereference information indicates a storage location within anintermediary volume for the metadata representation of the source data.4. The method of claim 3, wherein copying the metadata representation ofthe source data is dependent upon the reference information foridentifying the storage location within the intermediary volume thatstores the metadata representation of the source data.
 5. The method ofclaim 1, wherein the source data comprises a plurality of data objects,and wherein the method further comprises: responsive to a write requestdirected at a particular data object of the plurality of data objects,copying the particular data object from the source location in thesource volume to a target location within the target volume; whereincopying the particular data object uses the metadata representation ofthe source data to identify a source location of the particular dataobject within the source volume.
 6. The method of claim 5, furthercomprising: responsive to copying the particular data object from thesource volume to the target volume, updating the metadata representationof the source data stored in the target volume to indicate that theparticular data object is stored at the target location in the targetvolume instead of the source location in the source volume.
 7. Themethod of claim 5, wherein none of the plurality of data objects arecopied into the target volume until a given data object of the pluralityof data objects is modified within the source volume.
 8. The method ofclaim 1, wherein the metadata representation is a snapshot of the sourcedata, and wherein there is a single copy of the source data.
 9. Themethod of claim 1, wherein the intermediary volume is one of a pluralityof intermediary volumes.
 10. The method of claim 8, wherein thereference information comprises an intermediary volume identifier andoffset for locating the metadata representation.
 11. The method of claim8, wherein each respective metadata representations among a plurality ofmetadata representations is circulated among the plurality ofintermediary volumes according to a specified window of time.
 12. Themethod of claim 1 further comprising providing reference informationcorresponding to source data that is represented by a metadatarepresentation, the source data being stored within a source volume. 13.The method of claim 1 wherein copying, using the reference information,the metadata representation of the source data to the target volumeincludes copying the metadata representation from the source volume toan intermediary volume and copying the metadata representation from theintermediary volume to the target volume.
 14. An apparatus comprising acomputer processor, a computer memory operatively coupled to thecomputer processor, the computer memory having disposed within itcomputer program instructions that, when executed by the computerprocessor, cause the apparatus to carry out the steps of: receiving arequest to write the source data to a target volume, wherein the requestto write the source data indicates the reference information; obtaininga metadata representation of the source data using the referenceinformation; and copying, using the reference information, the metadatarepresentation of the source data to the target volume.
 15. Theapparatus of claim 14, wherein the metadata representation of the sourcedata is a structured collection of metadata objects referring,respectively, to data objects comprising the source data, and whereinthe data objects are stored within the source volume.
 16. The apparatusof claim 14, wherein the reference information indicates a storagelocation within the intermediary volume for the metadata representationof the source data.
 17. The apparatus of claim 14, wherein the sourcedata comprises a plurality of data objects, and wherein the apparatusfurther comprises computer program instructions that, when executed bythe computer processor, cause the apparatus to carry out the steps of:responsive to a write request directed at a particular data object ofthe plurality of data objects, copying the particular data object fromthe source location in the source volume to a target location within thetarget volume; wherein copying the particular data object uses themetadata representation of the source data to identify a source locationof the particular data object within the source volume.
 18. Theapparatus of claim 17, further comprising computer program instructionsthat, when executed by the computer processor, cause the apparatus tocarry out the step of, responsive to copying the particular data objectfrom the source volume to the target volume, updating the metadatarepresentation of the source data stored in the target volume toindicate that the particular data object is stored at the targetlocation in the target volume instead of the source location in thesource volume.
 19. The apparatus of claim 17, wherein none of theplurality of data objects are copied into the target volume until agiven data object of the plurality of data objects is modified withinthe source volume.
 20. A computer program product including a computerreadable storage medium having computer readable program instructionsthereon for causing a processor to carry out: receiving a request towrite the source data to a target volume, wherein the request to writethe source data indicates the reference information; obtaining themetadata representation of the source data using the referenceinformation; and copying, using the reference information, the metadatarepresentation of the source data to the target volume.